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 $63.64   3.787%   $66.05   $66.05   $66.05   $66.10  
  Purchase #2 $244.98   10.274%   $270.1492   $270.15   $270.15   $270.10  
  Purchase #3 $102.62   8.218%   $111.0533   $111.05   $111.05   $111.10  
  Purchase #4 $50.53   9.854%   $55.5092   $55.51   $55.50   $55.50  
  Purchase #5 $122.71   6.287%   $130.4248   $130.42   $130.40   $130.40  
  Purchase #6 $41.52   11.355%   $46.2346   $46.23   $46.25   $46.20  
  Purchase #7 $9.53   7.445%   $10.2395   $10.24   $10.25   $10.20  
  7 purchase totals = $635.53       $689.6606   $689.65   $689.65   $689.60