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 $186.84   3.397%   $193.187   $193.19   $193.20   $193.20  
  Purchase #2 $92.72   11.784%   $103.6461   $103.65   $103.65   $103.60  
  Purchase #3 $97.27   8.238%   $105.2831   $105.28   $105.30   $105.30  
  Purchase #4 $197.37   8.682%   $214.5057   $214.51   $214.50   $214.50  
  Purchase #5 $142.32   4.325%   $148.4753   $148.48   $148.50   $148.50  
  Purchase #6 $45.34   8.175%   $49.0465   $49.05   $49.05   $49.00  
  Purchase #7 $216.69   6.376%   $230.5062   $230.51   $230.50   $230.50  
  7 purchase totals = $978.55       $1,044.6499   $1,044.67   $1,044.70   $1,044.60