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 $89.42   6.549%   $95.2761   $95.28   $95.30   $95.30  
  Purchase #2 $241.43   9.810%   $265.1143   $265.11   $265.10   $265.10  
  Purchase #3 $72.61   9.598%   $79.5791   $79.58   $79.60   $79.60  
  Purchase #4 $193.56   12.828%   $218.3899   $218.39   $218.40   $218.40  
  Purchase #5 $206.92   12.496%   $232.7767   $232.78   $232.80   $232.80  
  Purchase #6 $43.67   13.170%   $49.4213   $49.42   $49.40   $49.40  
  Purchase #7 $26.47   13.339%   $30.0008   $30.00   $30.00   $30.00  
  7 purchase totals = $874.08       $970.5582   $970.56   $970.60   $970.60