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 $56.87   7.772%   $61.2899   $61.29   $61.30   $61.30  
  Purchase #2 $241.28   5.589%   $254.7651   $254.77   $254.75   $254.80  
  Purchase #3 $58.65   9.572%   $64.264   $64.26   $64.25   $64.30  
  Purchase #4 $31.59   5.454%   $33.3129   $33.31   $33.30   $33.30  
  Purchase #5 $140.41   10.527%   $155.191   $155.19   $155.20   $155.20  
  Purchase #6 $91.98   3.364%   $95.0742   $95.07   $95.05   $95.10  
  Purchase #7 $230.97   7.794%   $248.9718   $248.97   $248.95   $249.00  
  7 purchase totals = $851.75       $912.8689   $912.86   $912.80   $913.00