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 $49.42   8.802%   $53.7699   $53.77   $53.75   $53.80  
  Purchase #2 $126.55   4.752%   $132.5637   $132.56   $132.55   $132.60  
  Purchase #3 $14.84   3.387%   $15.3426   $15.34   $15.35   $15.30  
  Purchase #4 $157.73   8.400%   $170.9793   $170.98   $171.00   $171.00  
  Purchase #5 $165.35   9.772%   $181.508   $181.51   $181.50   $181.50  
  Purchase #6 $184.69   10.629%   $204.3207   $204.32   $204.30   $204.30  
  Purchase #7 $172.57   5.309%   $181.7317   $181.73   $181.75   $181.70  
  7 purchase totals = $871.15       $940.2159   $940.21   $940.20   $940.20