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 $48.51   13.400%   $55.0103   $55.01   $55.00   $55.00  
  Purchase #2 $30.69   12.537%   $34.5376   $34.54   $34.55   $34.50  
  Purchase #3 $11.66   10.310%   $12.8621   $12.86   $12.85   $12.90  
  Purchase #4 $84.82   7.739%   $91.3842   $91.38   $91.40   $91.40  
  Purchase #5 $209.37   6.855%   $223.7223   $223.72   $223.70   $223.70  
  Purchase #6 $244.74   9.575%   $268.1739   $268.17   $268.15   $268.20  
  Purchase #7 $243.33   9.459%   $266.3466   $266.35   $266.35   $266.30  
  7 purchase totals = $873.12       $952.0370   $952.03   $952.00   $952.00