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 $249.80   4.137%   $260.1342   $260.13   $260.15   $260.10  
  Purchase #2 $162.39   13.479%   $184.2785   $184.28   $184.30   $184.30  
  Purchase #3 $35.88   11.269%   $39.9233   $39.92   $39.90   $39.90  
  Purchase #4 $91.26   5.136%   $95.9471   $95.95   $95.95   $95.90  
  Purchase #5 $231.45   5.506%   $244.1936   $244.19   $244.20   $244.20  
  Purchase #6 $85.60   12.534%   $96.3291   $96.33   $96.35   $96.30  
  Purchase #7 $116.75   12.471%   $131.3099   $131.31   $131.30   $131.30  
  7 purchase totals = $973.13       $1,052.1157   $1,052.11   $1,052.15   $1,052.00