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 $204.40   13.265%   $231.5137   $231.51   $231.50   $231.50  
  Purchase #2 $56.68   6.382%   $60.2973   $60.30   $60.30   $60.30  
  Purchase #3 $158.43   11.234%   $176.228   $176.23   $176.25   $176.20  
  Purchase #4 $91.46   9.278%   $99.9457   $99.95   $99.95   $99.90  
  Purchase #5 $166.49   8.404%   $180.4818   $180.48   $180.50   $180.50  
  Purchase #6 $200.92   11.490%   $224.0057   $224.01   $224.00   $224.00  
  Purchase #7 $58.26   3.321%   $60.1948   $60.19   $60.20   $60.20  
  7 purchase totals = $936.64       $1,032.6670   $1,032.67   $1,032.70   $1,032.60