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 $176.98   10.707%   $195.9292   $195.93   $195.95   $195.90  
  Purchase #2 $24.26   4.220%   $25.2838   $25.28   $25.30   $25.30  
  Purchase #3 $218.92   7.217%   $234.7195   $234.72   $234.70   $234.70  
  Purchase #4 $39.46   13.431%   $44.7599   $44.76   $44.75   $44.80  
  Purchase #5 $73.50   7.228%   $78.8126   $78.81   $78.80   $78.80  
  Purchase #6 $25.45   5.657%   $26.8897   $26.89   $26.90   $26.90  
  Purchase #7 $64.65   4.302%   $67.4312   $67.43   $67.45   $67.40  
  7 purchase totals = $623.22       $673.8259   $673.82   $673.85   $673.80