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 $148.57   3.793%   $154.2053   $154.21   $154.20   $154.20  
  Purchase #2 $118.94   12.470%   $133.7718   $133.77   $133.75   $133.80  
  Purchase #3 $11.66   6.235%   $12.387   $12.39   $12.40   $12.40  
  Purchase #4 $131.35   10.603%   $145.277   $145.28   $145.30   $145.30  
  Purchase #5 $224.62   10.760%   $248.7891   $248.79   $248.80   $248.80  
  Purchase #6 $202.59   5.295%   $213.3171   $213.32   $213.30   $213.30  
  Purchase #7 $46.98   4.219%   $48.9621   $48.96   $48.95   $49.00  
  7 purchase totals = $884.71       $956.7094   $956.72   $956.70   $956.80