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 $62.43   8.485%   $67.7272   $67.73   $67.75   $67.70  
  Purchase #2 $23.34   4.338%   $24.3525   $24.35   $24.35   $24.40  
  Purchase #3 $15.63   10.611%   $17.2885   $17.29   $17.30   $17.30  
  Purchase #4 $48.29   4.370%   $50.4003   $50.40   $50.40   $50.40  
  Purchase #5 $145.77   4.855%   $152.8471   $152.85   $152.85   $152.80  
  Purchase #6 $160.83   9.221%   $175.6601   $175.66   $175.65   $175.70  
  Purchase #7 $117.54   4.707%   $123.0726   $123.07   $123.05   $123.10  
  7 purchase totals = $573.83       $611.3483   $611.35   $611.35   $611.40