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 $87.30   13.330%   $98.9371   $98.94   $98.95   $98.90  
  Purchase #2 $147.82   8.654%   $160.6123   $160.61   $160.60   $160.60  
  Purchase #3 $220.26   9.161%   $240.438   $240.44   $240.45   $240.40  
  Purchase #4 $114.29   6.219%   $121.3977   $121.40   $121.40   $121.40  
  Purchase #5 $116.40   10.503%   $128.6255   $128.63   $128.65   $128.60  
  Purchase #6 $29.61   13.114%   $33.4931   $33.49   $33.50   $33.50  
  Purchase #7 $81.57   10.661%   $90.2662   $90.27   $90.25   $90.30  
  7 purchase totals = $797.25       $873.7699   $873.78   $873.80   $873.70