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 $241.91   11.259%   $269.1466   $269.15   $269.15   $269.10  
  Purchase #2 $11.73   4.200%   $12.2227   $12.22   $12.20   $12.20  
  Purchase #3 $25.65   9.586%   $28.1088   $28.11   $28.10   $28.10  
  Purchase #4 $244.53   4.380%   $255.2404   $255.24   $255.25   $255.20  
  Purchase #5 $114.57   9.807%   $125.8059   $125.81   $125.80   $125.80  
  Purchase #6 $205.52   3.189%   $212.074   $212.07   $212.05   $212.10  
  Purchase #7 $21.98   6.564%   $23.4228   $23.42   $23.40   $23.40  
  7 purchase totals = $865.89       $926.0212   $926.02   $925.95   $925.90