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 $117.78   4.444%   $123.0141   $123.01   $123.00   $123.00  
  Purchase #2 $238.55   3.479%   $246.8492   $246.85   $246.85   $246.80  
  Purchase #3 $215.36   13.222%   $243.8349   $243.83   $243.85   $243.80  
  Purchase #4 $221.91   3.592%   $229.881   $229.88   $229.90   $229.90  
  Purchase #5 $128.55   10.675%   $142.2727   $142.27   $142.25   $142.30  
  Purchase #6 $145.80   3.775%   $151.304   $151.30   $151.30   $151.30  
  Purchase #7 $59.80   7.715%   $64.4136   $64.41   $64.40   $64.40  
  7 purchase totals = $1,127.75       $1,201.5695   $1,201.55   $1,201.55   $1,201.50