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 $91.28   3.628%   $94.5916   $94.59   $94.60   $94.60  
  Purchase #2 $66.38   9.400%   $72.6197   $72.62   $72.60   $72.60  
  Purchase #3 $166.59   6.124%   $176.792   $176.79   $176.80   $176.80  
  Purchase #4 $121.71   12.443%   $136.8544   $136.85   $136.85   $136.90  
  Purchase #5 $109.29   11.738%   $122.1185   $122.12   $122.10   $122.10  
  Purchase #6 $24.84   3.753%   $25.7722   $25.77   $25.75   $25.80  
  Purchase #7 $59.99   11.607%   $66.953   $66.95   $66.95   $67.00  
  7 purchase totals = $640.08       $695.7014   $695.69   $695.65   $695.80