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 $59.45   4.416%   $62.0753   $62.08   $62.10   $62.10  
  Purchase #2 $81.67   13.823%   $92.9592   $92.96   $92.95   $93.00  
  Purchase #3 $188.58   3.446%   $195.0785   $195.08   $195.10   $195.10  
  Purchase #4 $175.63   12.474%   $197.5381   $197.54   $197.55   $197.50  
  Purchase #5 $75.98   13.443%   $86.194   $86.19   $86.20   $86.20  
  Purchase #6 $113.93   13.711%   $129.5509   $129.55   $129.55   $129.60  
  Purchase #7 $202.84   6.575%   $216.1767   $216.18   $216.20   $216.20  
  7 purchase totals = $898.08       $979.5727   $979.58   $979.65   $979.70