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 $84.93   9.224%   $92.7639   $92.76   $92.75   $92.80  
  Purchase #2 $234.37   12.235%   $263.0452   $263.05   $263.05   $263.00  
  Purchase #3 $25.90   12.693%   $29.1875   $29.19   $29.20   $29.20  
  Purchase #4 $238.51   7.327%   $255.9856   $255.99   $256.00   $256.00  
  Purchase #5 $148.96   8.592%   $161.7586   $161.76   $161.75   $161.80  
  Purchase #6 $126.26   13.810%   $143.6965   $143.70   $143.70   $143.70  
  Purchase #7 $97.54   6.323%   $103.7075   $103.71   $103.70   $103.70  
  7 purchase totals = $956.47       $1,050.1448   $1,050.16   $1,050.15   $1,050.20