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 $208.51   8.272%   $225.7579   $225.76   $225.75   $225.80  
  Purchase #2 $139.25   7.436%   $149.6046   $149.60   $149.60   $149.60  
  Purchase #3 $61.45   4.853%   $64.4322   $64.43   $64.45   $64.40  
  Purchase #4 $248.28   11.299%   $276.3332   $276.33   $276.35   $276.30  
  Purchase #5 $230.72   8.596%   $250.5527   $250.55   $250.55   $250.60  
  Purchase #6 $239.72   13.589%   $272.2956   $272.30   $272.30   $272.30  
  Purchase #7 $199.45   6.445%   $212.3046   $212.30   $212.30   $212.30  
  7 purchase totals = $1,327.38       $1,451.2808   $1,451.27   $1,451.30   $1,451.30