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 $206.87   11.269%   $230.1822   $230.18   $230.20   $230.20  
  Purchase #2 $25.33   3.685%   $26.2634   $26.26   $26.25   $26.30  
  Purchase #3 $180.56   4.221%   $188.1814   $188.18   $188.20   $188.20  
  Purchase #4 $71.61   8.712%   $77.8487   $77.85   $77.85   $77.80  
  Purchase #5 $78.93   10.870%   $87.5097   $87.51   $87.50   $87.50  
  Purchase #6 $229.40   11.599%   $256.0081   $256.01   $256.00   $256.00  
  Purchase #7 $210.91   9.505%   $230.957   $230.96   $230.95   $231.00  
  7 purchase totals = $1,003.61       $1,096.9505   $1,096.95   $1,096.95   $1,097.00