Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $135.97   11.168%   $151.1551   $151.16   $151.15   $151.20  
  Purchase #2 $160.43   8.197%   $173.5804   $173.58   $173.60   $173.60  
  Purchase #3 $227.27   8.231%   $245.9766   $245.98   $246.00   $246.00  
  Purchase #4 $233.43   4.352%   $243.5889   $243.59   $243.60   $243.60  
  Purchase #5 $148.94   11.109%   $165.4857   $165.49   $165.50   $165.50  
  Purchase #6 $183.88   13.223%   $208.1945   $208.19   $208.20   $208.20  
  Purchase #7 $164.77   8.336%   $178.5052   $178.51   $178.50   $178.50  
  7 purchase totals = $1,254.69       $1,366.4864   $1,366.50   $1,366.55   $1,366.60