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 $94.60   3.867%   $98.2582   $98.26   $98.25   $98.30  
  Purchase #2 $214.84   7.239%   $230.3923   $230.39   $230.40   $230.40  
  Purchase #3 $66.47   3.561%   $68.837   $68.84   $68.85   $68.80  
  Purchase #4 $134.53   8.325%   $145.7296   $145.73   $145.75   $145.70  
  Purchase #5 $185.73   6.669%   $198.1163   $198.12   $198.10   $198.10  
  Purchase #6 $214.78   9.635%   $235.4741   $235.47   $235.45   $235.50  
  Purchase #7 $22.35   12.732%   $25.1956   $25.20   $25.20   $25.20  
  7 purchase totals = $933.30       $1,002.0031   $1,002.01   $1,002.00   $1,002.00