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 $59.29   13.749%   $67.4418   $67.44   $67.45   $67.40  
  Purchase #2 $169.97   8.448%   $184.3291   $184.33   $184.35   $184.30  
  Purchase #3 $184.84   5.766%   $195.4979   $195.50   $195.50   $195.50  
  Purchase #4 $196.30   8.400%   $212.7892   $212.79   $212.80   $212.80  
  Purchase #5 $105.99   4.449%   $110.7055   $110.71   $110.70   $110.70  
  Purchase #6 $56.86   10.336%   $62.737   $62.74   $62.75   $62.70  
  Purchase #7 $106.55   13.798%   $121.2518   $121.25   $121.25   $121.30  
  7 purchase totals = $879.80       $954.7523   $954.76   $954.80   $954.70