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 $156.67   6.868%   $167.4301   $167.43   $167.45   $167.40  
  Purchase #2 $26.29   8.381%   $28.4934   $28.49   $28.50   $28.50  
  Purchase #3 $65.55   11.391%   $73.0168   $73.02   $73.00   $73.00  
  Purchase #4 $193.73   4.695%   $202.8256   $202.83   $202.85   $202.80  
  Purchase #5 $64.49   12.816%   $72.755   $72.76   $72.75   $72.80  
  Purchase #6 $88.31   6.176%   $93.764   $93.76   $93.75   $93.80  
  Purchase #7 $212.54   6.867%   $227.1351   $227.14   $227.15   $227.10  
  7 purchase totals = $807.58       $865.4200   $865.43   $865.45   $865.40