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 $87.68   11.367%   $97.6466   $97.65   $97.65   $97.60  
  Purchase #2 $230.83   13.659%   $262.3591   $262.36   $262.35   $262.40  
  Purchase #3 $121.60   9.701%   $133.3964   $133.40   $133.40   $133.40  
  Purchase #4 $174.78   7.534%   $187.9479   $187.95   $187.95   $187.90  
  Purchase #5 $79.75   13.747%   $90.7132   $90.71   $90.70   $90.70  
  Purchase #6 $245.97   8.154%   $266.0264   $266.03   $266.05   $266.00  
  Purchase #7 $35.47   13.736%   $40.3422   $40.34   $40.35   $40.30  
  7 purchase totals = $976.08       $1,078.4318   $1,078.44   $1,078.45   $1,078.30