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 $58.79   13.724%   $66.8583   $66.86   $66.85   $66.90  
  Purchase #2 $228.49   13.471%   $259.2699   $259.27   $259.25   $259.30  
  Purchase #3 $221.26   10.708%   $244.9525   $244.95   $244.95   $245.00  
  Purchase #4 $47.87   9.821%   $52.5713   $52.57   $52.55   $52.60  
  Purchase #5 $159.87   7.799%   $172.3383   $172.34   $172.35   $172.30  
  Purchase #6 $69.56   7.790%   $74.9787   $74.98   $75.00   $75.00  
  Purchase #7 $224.37   13.695%   $255.0975   $255.10   $255.10   $255.10  
  7 purchase totals = $1,010.21       $1,126.0665   $1,126.07   $1,126.05   $1,126.20