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 $76.40   13.321%   $86.5772   $86.58   $86.60   $86.60  
  Purchase #2 $149.45   13.674%   $169.8858   $169.89   $169.90   $169.90  
  Purchase #3 $250.63   8.764%   $272.5952   $272.60   $272.60   $272.60  
  Purchase #4 $66.44   8.730%   $72.2402   $72.24   $72.25   $72.20  
  Purchase #5 $177.95   13.558%   $202.0765   $202.08   $202.10   $202.10  
  Purchase #6 $197.43   4.413%   $206.1426   $206.14   $206.15   $206.10  
  Purchase #7 $23.98   3.517%   $24.8234   $24.82   $24.80   $24.80  
  7 purchase totals = $942.28       $1,034.3409   $1,034.35   $1,034.40   $1,034.30