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 $125.82   5.156%   $132.3073   $132.31   $132.30   $132.30  
  Purchase #2 $179.68   12.122%   $201.4608   $201.46   $201.45   $201.50  
  Purchase #3 $231.76   13.843%   $263.8425   $263.84   $263.85   $263.80  
  Purchase #4 $69.92   8.375%   $75.7758   $75.78   $75.80   $75.80  
  Purchase #5 $238.85   13.470%   $271.0231   $271.02   $271.00   $271.00  
  Purchase #6 $114.41   10.241%   $126.1267   $126.13   $126.15   $126.10  
  Purchase #7 $39.50   6.316%   $41.9948   $41.99   $42.00   $42.00  
  7 purchase totals = $999.94       $1,112.5310   $1,112.53   $1,112.55   $1,112.50