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 $211.64   6.562%   $225.5278   $225.53   $225.55   $225.50  
  Purchase #2 $41.49   10.244%   $45.7402   $45.74   $45.75   $45.70  
  Purchase #3 $87.29   4.711%   $91.4022   $91.40   $91.40   $91.40  
  Purchase #4 $43.36   10.864%   $48.0706   $48.07   $48.05   $48.10  
  Purchase #5 $219.43   4.316%   $228.9006   $228.90   $228.90   $228.90  
  Purchase #6 $62.57   3.791%   $64.942   $64.94   $64.95   $64.90  
  Purchase #7 $193.86   4.163%   $201.9304   $201.93   $201.95   $201.90  
  7 purchase totals = $859.64       $906.5138   $906.51   $906.55   $906.40