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 $170.50   12.740%   $192.2217   $192.22   $192.20   $192.20  
  Purchase #2 $193.78   13.555%   $220.0469   $220.05   $220.05   $220.00  
  Purchase #3 $195.46   7.440%   $210.0022   $210.00   $210.00   $210.00  
  Purchase #4 $76.54   3.152%   $78.9525   $78.95   $78.95   $79.00  
  Purchase #5 $93.62   12.240%   $105.0791   $105.08   $105.10   $105.10  
  Purchase #6 $134.59   11.367%   $149.8888   $149.89   $149.90   $149.90  
  Purchase #7 $17.76   13.336%   $20.1285   $20.13   $20.15   $20.10  
  7 purchase totals = $882.25       $976.3197   $976.32   $976.35   $976.30