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 $41.54   4.603%   $43.4521   $43.45   $43.45   $43.50  
  Purchase #2 $167.44   6.498%   $178.3203   $178.32   $178.30   $178.30  
  Purchase #3 $205.25   6.656%   $218.9114   $218.91   $218.90   $218.90  
  Purchase #4 $153.96   11.607%   $171.8301   $171.83   $171.85   $171.80  
  Purchase #5 $112.26   7.427%   $120.5976   $120.60   $120.60   $120.60  
  Purchase #6 $201.38   12.817%   $227.1909   $227.19   $227.20   $227.20  
  Purchase #7 $47.62   9.459%   $52.1244   $52.12   $52.10   $52.10  
  7 purchase totals = $929.45       $1,012.4268   $1,012.42   $1,012.40   $1,012.40