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 $56.93   11.822%   $63.6603   $63.66   $63.65   $63.70  
  Purchase #2 $174.33   9.194%   $190.3579   $190.36   $190.35   $190.40  
  Purchase #3 $117.77   13.767%   $133.9834   $133.98   $134.00   $134.00  
  Purchase #4 $117.51   13.644%   $133.5431   $133.54   $133.55   $133.50  
  Purchase #5 $111.33   12.302%   $125.0258   $125.03   $125.05   $125.00  
  Purchase #6 $140.96   12.837%   $159.055   $159.06   $159.05   $159.10  
  Purchase #7 $112.62   7.519%   $121.0879   $121.09   $121.10   $121.10  
  7 purchase totals = $831.45       $926.7134   $926.72   $926.75   $926.80