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 $67.86   12.281%   $76.1939   $76.19   $76.20   $76.20  
  Purchase #2 $26.46   9.263%   $28.911   $28.91   $28.90   $28.90  
  Purchase #3 $182.51   10.177%   $201.084   $201.08   $201.10   $201.10  
  Purchase #4 $183.56   13.793%   $208.8784   $208.88   $208.90   $208.90  
  Purchase #5 $77.40   13.229%   $87.6392   $87.64   $87.65   $87.60  
  Purchase #6 $102.77   11.492%   $114.5803   $114.58   $114.60   $114.60  
  Purchase #7 $42.49   3.611%   $44.0243   $44.02   $44.00   $44.00  
  7 purchase totals = $683.05       $761.3111   $761.30   $761.35   $761.30