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 $116.92   10.629%   $129.3474   $129.35   $129.35   $129.30  
  Purchase #2 $227.85   4.571%   $238.265   $238.27   $238.25   $238.30  
  Purchase #3 $58.82   3.694%   $60.9928   $60.99   $61.00   $61.00  
  Purchase #4 $216.29   7.405%   $232.3063   $232.31   $232.30   $232.30  
  Purchase #5 $142.65   4.600%   $149.2119   $149.21   $149.20   $149.20  
  Purchase #6 $207.61   3.203%   $214.2597   $214.26   $214.25   $214.30  
  Purchase #7 $162.52   10.619%   $179.778   $179.78   $179.80   $179.80  
  7 purchase totals = $1,132.66       $1,204.1611   $1,204.17   $1,204.15   $1,204.20