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 $68.28   8.663%   $74.1951   $74.20   $74.20   $74.20  
  Purchase #2 $39.48   12.425%   $44.3854   $44.39   $44.40   $44.40  
  Purchase #3 $60.70   8.378%   $65.7854   $65.79   $65.80   $65.80  
  Purchase #4 $136.84   11.253%   $152.2386   $152.24   $152.25   $152.20  
  Purchase #5 $7.70   6.240%   $8.1805   $8.18   $8.20   $8.20  
  Purchase #6 $235.94   12.763%   $266.053   $266.05   $266.05   $266.10  
  Purchase #7 $131.48   7.386%   $141.1911   $141.19   $141.20   $141.20  
  7 purchase totals = $680.42       $752.0291   $752.04   $752.10   $752.10