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 $141.97   4.772%   $148.7448   $148.74   $148.75   $148.70  
  Purchase #2 $37.26   10.739%   $41.2614   $41.26   $41.25   $41.30  
  Purchase #3 $57.41   13.145%   $64.9565   $64.96   $64.95   $65.00  
  Purchase #4 $224.95   11.145%   $250.0207   $250.02   $250.00   $250.00  
  Purchase #5 $181.38   3.539%   $187.799   $187.80   $187.80   $187.80  
  Purchase #6 $238.52   9.855%   $262.0261   $262.03   $262.05   $262.00  
  Purchase #7 $76.70   12.790%   $86.5099   $86.51   $86.50   $86.50  
  7 purchase totals = $958.19       $1,041.3184   $1,041.32   $1,041.30   $1,041.30