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 $246.34   6.652%   $262.7265   $262.73   $262.75   $262.70  
  Purchase #2 $193.61   6.500%   $206.1947   $206.19   $206.20   $206.20  
  Purchase #3 $156.31   8.275%   $169.2447   $169.24   $169.25   $169.20  
  Purchase #4 $195.75   5.386%   $206.2931   $206.29   $206.30   $206.30  
  Purchase #5 $128.55   4.809%   $134.732   $134.73   $134.75   $134.70  
  Purchase #6 $134.69   9.563%   $147.5704   $147.57   $147.55   $147.60  
  Purchase #7 $134.75   9.124%   $147.0446   $147.04   $147.05   $147.00  
  7 purchase totals = $1,190.00       $1,273.8060   $1,273.79   $1,273.85   $1,273.70