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 $77.36   7.380%   $83.0692   $83.07   $83.05   $83.10  
  Purchase #2 $72.46   7.360%   $77.7931   $77.79   $77.80   $77.80  
  Purchase #3 $121.44   10.245%   $133.8815   $133.88   $133.90   $133.90  
  Purchase #4 $141.26   7.771%   $152.2373   $152.24   $152.25   $152.20  
  Purchase #5 $67.63   7.786%   $72.8957   $72.90   $72.90   $72.90  
  Purchase #6 $166.78   13.451%   $189.2136   $189.21   $189.20   $189.20  
  Purchase #7 $87.44   12.431%   $98.3097   $98.31   $98.30   $98.30  
  7 purchase totals = $734.37       $807.4001   $807.40   $807.40   $807.40