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 $32.63   3.642%   $33.8184   $33.82   $33.80   $33.80  
  Purchase #2 $89.53   13.873%   $101.9505   $101.95   $101.95   $102.00  
  Purchase #3 $242.60   13.389%   $275.0817   $275.08   $275.10   $275.10  
  Purchase #4 $176.58   12.235%   $198.1846   $198.18   $198.20   $198.20  
  Purchase #5 $19.68   5.276%   $20.7183   $20.72   $20.70   $20.70  
  Purchase #6 $247.74   6.566%   $264.0066   $264.01   $264.00   $264.00  
  Purchase #7 $93.48   11.265%   $104.0105   $104.01   $104.00   $104.00  
  7 purchase totals = $902.24       $997.7706   $997.77   $997.75   $997.80