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 $49.78   13.670%   $56.5849   $56.58   $56.60   $56.60  
  Purchase #2 $91.55   3.145%   $94.4292   $94.43   $94.45   $94.40  
  Purchase #3 $202.35   4.164%   $210.7759   $210.78   $210.80   $210.80  
  Purchase #4 $152.79   4.289%   $159.3432   $159.34   $159.35   $159.30  
  Purchase #5 $248.90   10.869%   $275.9529   $275.95   $275.95   $276.00  
  Purchase #6 $128.99   8.772%   $140.305   $140.31   $140.30   $140.30  
  Purchase #7 $106.28   11.818%   $118.8402   $118.84   $118.85   $118.80  
  7 purchase totals = $980.64       $1,056.2313   $1,056.23   $1,056.30   $1,056.20