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 $42.79   12.753%   $48.247   $48.25   $48.25   $48.20  
  Purchase #2 $189.85   5.542%   $200.3715   $200.37   $200.35   $200.40  
  Purchase #3 $197.39   4.295%   $205.8679   $205.87   $205.85   $205.90  
  Purchase #4 $14.72   11.526%   $16.4166   $16.42   $16.40   $16.40  
  Purchase #5 $234.75   9.363%   $256.7296   $256.73   $256.75   $256.70  
  Purchase #6 $200.69   12.422%   $225.6197   $225.62   $225.60   $225.60  
  Purchase #7 $114.51   3.846%   $118.9141   $118.91   $118.90   $118.90  
  7 purchase totals = $994.70       $1,072.1664   $1,072.17   $1,072.10   $1,072.10