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 $84.56   12.495%   $95.1258   $95.13   $95.15   $95.10  
  Purchase #2 $43.68   6.671%   $46.5939   $46.59   $46.60   $46.60  
  Purchase #3 $43.65   12.443%   $49.0814   $49.08   $49.10   $49.10  
  Purchase #4 $122.69   6.487%   $130.6489   $130.65   $130.65   $130.60  
  Purchase #5 $208.94   7.772%   $225.1788   $225.18   $225.20   $225.20  
  Purchase #6 $235.86   7.401%   $253.316   $253.32   $253.30   $253.30  
  Purchase #7 $59.73   9.434%   $65.3649   $65.36   $65.35   $65.40  
  7 purchase totals = $799.11       $865.3097   $865.31   $865.35   $865.30