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 $53.83   11.264%   $59.8934   $59.89   $59.90   $59.90  
  Purchase #2 $205.72   12.757%   $231.9637   $231.96   $231.95   $232.00  
  Purchase #3 $12.62   11.664%   $14.092   $14.09   $14.10   $14.10  
  Purchase #4 $212.33   9.272%   $232.0172   $232.02   $232.00   $232.00  
  Purchase #5 $18.41   10.804%   $20.399   $20.40   $20.40   $20.40  
  Purchase #6 $163.91   5.346%   $172.6726   $172.67   $172.65   $172.70  
  Purchase #7 $171.89   13.556%   $195.1914   $195.19   $195.20   $195.20  
  7 purchase totals = $838.71       $926.2293   $926.22   $926.20   $926.30