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 $182.53   11.760%   $203.9955   $204.00   $204.00   $204.00  
  Purchase #2 $34.36   11.778%   $38.4069   $38.41   $38.40   $38.40  
  Purchase #3 $111.73   4.112%   $116.3243   $116.32   $116.30   $116.30  
  Purchase #4 $83.55   11.295%   $92.987   $92.99   $93.00   $93.00  
  Purchase #5 $163.39   12.372%   $183.6046   $183.60   $183.60   $183.60  
  Purchase #6 $236.45   13.769%   $269.0068   $269.01   $269.00   $269.00  
  Purchase #7 $44.81   10.122%   $49.3457   $49.35   $49.35   $49.30  
  7 purchase totals = $856.82       $953.6708   $953.68   $953.65   $953.60