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 $119.96   10.541%   $132.605   $132.61   $132.60   $132.60  
  Purchase #2 $213.59   11.819%   $238.8342   $238.83   $238.85   $238.80  
  Purchase #3 $116.32   4.412%   $121.452   $121.45   $121.45   $121.50  
  Purchase #4 $155.57   11.587%   $173.5959   $173.60   $173.60   $173.60  
  Purchase #5 $232.67   9.165%   $253.9942   $253.99   $254.00   $254.00  
  Purchase #6 $174.95   9.548%   $191.6542   $191.65   $191.65   $191.70  
  Purchase #7 $121.41   3.352%   $125.4797   $125.48   $125.50   $125.50  
  7 purchase totals = $1,134.47       $1,237.6152   $1,237.61   $1,237.65   $1,237.70