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 $225.42   8.820%   $245.302   $245.30   $245.30   $245.30  
  Purchase #2 $168.39   8.770%   $183.1578   $183.16   $183.15   $183.20  
  Purchase #3 $229.29   5.304%   $241.4515   $241.45   $241.45   $241.50  
  Purchase #4 $114.59   10.647%   $126.7904   $126.79   $126.80   $126.80  
  Purchase #5 $84.41   9.391%   $92.3369   $92.34   $92.35   $92.30  
  Purchase #6 $181.84   11.715%   $203.1426   $203.14   $203.15   $203.10  
  Purchase #7 $250.95   8.862%   $273.1892   $273.19   $273.20   $273.20  
  7 purchase totals = $1,254.89       $1,365.3704   $1,365.37   $1,365.40   $1,365.40