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 $164.43   13.497%   $186.6231   $186.62   $186.60   $186.60  
  Purchase #2 $97.82   11.206%   $108.7817   $108.78   $108.80   $108.80  
  Purchase #3 $49.99   8.627%   $54.3026   $54.30   $54.30   $54.30  
  Purchase #4 $111.96   10.560%   $123.783   $123.78   $123.80   $123.80  
  Purchase #5 $64.58   3.757%   $67.0063   $67.01   $67.00   $67.00  
  Purchase #6 $15.39   10.847%   $17.0594   $17.06   $17.05   $17.10  
  Purchase #7 $127.54   8.297%   $138.122   $138.12   $138.10   $138.10  
  7 purchase totals = $631.71       $695.6781   $695.67   $695.65   $695.70