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 $227.37   6.830%   $242.8994   $242.90   $242.90   $242.90  
  Purchase #2 $156.69   3.803%   $162.6489   $162.65   $162.65   $162.60  
  Purchase #3 $51.64   12.421%   $58.0542   $58.05   $58.05   $58.10  
  Purchase #4 $183.66   13.703%   $208.8269   $208.83   $208.85   $208.80  
  Purchase #5 $160.44   7.559%   $172.5677   $172.57   $172.55   $172.60  
  Purchase #6 $220.78   11.856%   $246.9557   $246.96   $246.95   $247.00  
  Purchase #7 $232.31   11.495%   $259.014   $259.01   $259.00   $259.00  
  7 purchase totals = $1,232.89       $1,350.9668   $1,350.97   $1,350.95   $1,351.00