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 $100.84   9.855%   $110.7778   $110.78   $110.80   $110.80  
  Purchase #2 $89.95   7.683%   $96.8609   $96.86   $96.85   $96.90  
  Purchase #3 $225.43   10.308%   $248.6673   $248.67   $248.65   $248.70  
  Purchase #4 $149.98   10.729%   $166.0714   $166.07   $166.05   $166.10  
  Purchase #5 $13.82   3.223%   $14.2654   $14.27   $14.25   $14.30  
  Purchase #6 $180.79   7.441%   $194.2426   $194.24   $194.25   $194.20  
  Purchase #7 $50.58   6.113%   $53.672   $53.67   $53.65   $53.70  
  7 purchase totals = $811.39       $884.5574   $884.56   $884.50   $884.70