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 $181.97   13.181%   $205.9555   $205.96   $205.95   $206.00  
  Purchase #2 $108.50   7.392%   $116.5203   $116.52   $116.50   $116.50  
  Purchase #3 $149.57   3.468%   $154.7571   $154.76   $154.75   $154.80  
  Purchase #4 $46.42   12.136%   $52.0535   $52.05   $52.05   $52.10  
  Purchase #5 $39.55   11.114%   $43.9456   $43.95   $43.95   $43.90  
  Purchase #6 $153.40   9.180%   $167.4821   $167.48   $167.50   $167.50  
  Purchase #7 $69.39   5.630%   $73.2967   $73.30   $73.30   $73.30  
  7 purchase totals = $748.80       $814.0108   $814.02   $814.00   $814.10