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 $55.31   11.849%   $61.8637   $61.86   $61.85   $61.90  
  Purchase #2 $42.86   13.160%   $48.5004   $48.50   $48.50   $48.50  
  Purchase #3 $125.51   6.241%   $133.3431   $133.34   $133.35   $133.30  
  Purchase #4 $63.64   5.426%   $67.0931   $67.09   $67.10   $67.10  
  Purchase #5 $25.47   10.692%   $28.1933   $28.19   $28.20   $28.20  
  Purchase #6 $215.49   12.339%   $242.0793   $242.08   $242.10   $242.10  
  Purchase #7 $179.77   12.212%   $201.7235   $201.72   $201.70   $201.70  
  7 purchase totals = $708.05       $782.7964   $782.78   $782.80   $782.80