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 $135.76   9.643%   $148.8513   $148.85   $148.85   $148.90  
  Purchase #2 $196.66   4.144%   $204.8096   $204.81   $204.80   $204.80  
  Purchase #3 $59.95   9.327%   $65.5415   $65.54   $65.55   $65.50  
  Purchase #4 $95.71   11.826%   $107.0287   $107.03   $107.05   $107.00  
  Purchase #5 $124.40   9.189%   $135.8311   $135.83   $135.85   $135.80  
  Purchase #6 $240.85   9.343%   $263.3526   $263.35   $263.35   $263.40  
  Purchase #7 $202.34   11.480%   $225.5686   $225.57   $225.55   $225.60  
  7 purchase totals = $1,055.67       $1,150.9834   $1,150.98   $1,151.00   $1,151.00