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 $220.91   11.741%   $246.847   $246.85   $246.85   $246.80  
  Purchase #2 $198.56   13.171%   $224.7123   $224.71   $224.70   $224.70  
  Purchase #3 $55.63   5.301%   $58.5789   $58.58   $58.60   $58.60  
  Purchase #4 $170.25   7.251%   $182.5948   $182.59   $182.60   $182.60  
  Purchase #5 $144.99   11.485%   $161.6421   $161.64   $161.65   $161.60  
  Purchase #6 $181.56   5.548%   $191.6329   $191.63   $191.65   $191.60  
  Purchase #7 $5.54   12.271%   $6.2198   $6.22   $6.20   $6.20  
  7 purchase totals = $977.44       $1,072.2278   $1,072.22   $1,072.25   $1,072.10