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 $85.49   13.226%   $96.7969   $96.80   $96.80   $96.80  
  Purchase #2 $51.57   4.805%   $54.0479   $54.05   $54.05   $54.00  
  Purchase #3 $142.53   4.714%   $149.2489   $149.25   $149.25   $149.20  
  Purchase #4 $99.92   9.354%   $109.2665   $109.27   $109.25   $109.30  
  Purchase #5 $29.65   13.385%   $33.6187   $33.62   $33.60   $33.60  
  Purchase #6 $236.90   11.311%   $263.6958   $263.70   $263.70   $263.70  
  Purchase #7 $142.78   12.827%   $161.0944   $161.09   $161.10   $161.10  
  7 purchase totals = $788.84       $867.7691   $867.78   $867.75   $867.70