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 $212.27   7.705%   $228.6254   $228.63   $228.65   $228.60  
  Purchase #2 $166.29   9.152%   $181.5089   $181.51   $181.50   $181.50  
  Purchase #3 $59.86   7.714%   $64.4776   $64.48   $64.50   $64.50  
  Purchase #4 $120.83   10.226%   $133.1861   $133.19   $133.20   $133.20  
  Purchase #5 $69.25   6.557%   $73.7907   $73.79   $73.80   $73.80  
  Purchase #6 $138.86   8.867%   $151.1727   $151.17   $151.15   $151.20  
  Purchase #7 $63.92   12.661%   $72.0129   $72.01   $72.00   $72.00  
  7 purchase totals = $831.28       $904.7743   $904.78   $904.80   $904.80