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 $77.49   8.201%   $83.845   $83.85   $83.85   $83.80  
  Purchase #2 $71.47   4.471%   $74.6654   $74.67   $74.65   $74.70  
  Purchase #3 $97.41   11.747%   $108.8528   $108.85   $108.85   $108.90  
  Purchase #4 $116.73   9.371%   $127.6688   $127.67   $127.65   $127.70  
  Purchase #5 $51.34   4.365%   $53.581   $53.58   $53.60   $53.60  
  Purchase #6 $63.52   6.302%   $67.523   $67.52   $67.50   $67.50  
  Purchase #7 $138.84   13.780%   $157.9722   $157.97   $157.95   $158.00  
  7 purchase totals = $616.80       $674.1082   $674.11   $674.05   $674.20