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 $237.67   6.590%   $253.3325   $253.33   $253.35   $253.30  
  Purchase #2 $246.87   12.399%   $277.4794   $277.48   $277.50   $277.50  
  Purchase #3 $167.53   5.377%   $176.5381   $176.54   $176.55   $176.50  
  Purchase #4 $26.28   7.215%   $28.1761   $28.18   $28.20   $28.20  
  Purchase #5 $83.71   7.827%   $90.262   $90.26   $90.25   $90.30  
  Purchase #6 $209.91   12.663%   $236.4909   $236.49   $236.50   $236.50  
  Purchase #7 $11.89   11.763%   $13.2886   $13.29   $13.30   $13.30  
  7 purchase totals = $983.86       $1,075.5676   $1,075.57   $1,075.65   $1,075.60