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 $162.74   10.647%   $180.0669   $180.07   $180.05   $180.10  
  Purchase #2 $21.45   6.282%   $22.7975   $22.80   $22.80   $22.80  
  Purchase #3 $219.34   6.220%   $232.9829   $232.98   $233.00   $233.00  
  Purchase #4 $117.27   7.652%   $126.2435   $126.24   $126.25   $126.20  
  Purchase #5 $141.29   11.419%   $157.4239   $157.42   $157.40   $157.40  
  Purchase #6 $158.26   11.619%   $176.6482   $176.65   $176.65   $176.60  
  Purchase #7 $54.81   7.193%   $58.7525   $58.75   $58.75   $58.80  
  7 purchase totals = $875.16       $954.9154   $954.91   $954.90   $954.90