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 $68.58   7.766%   $73.9059   $73.91   $73.90   $73.90  
  Purchase #2 $216.95   13.356%   $245.9258   $245.93   $245.95   $245.90  
  Purchase #3 $141.65   10.532%   $156.5686   $156.57   $156.55   $156.60  
  Purchase #4 $123.74   9.569%   $135.5807   $135.58   $135.60   $135.60  
  Purchase #5 $212.76   6.334%   $226.2362   $226.24   $226.25   $226.20  
  Purchase #6 $9.54   13.815%   $10.858   $10.86   $10.85   $10.90  
  Purchase #7 $84.75   7.468%   $91.0791   $91.08   $91.10   $91.10  
  7 purchase totals = $857.97       $940.1543   $940.17   $940.20   $940.20