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 $51.67   13.842%   $58.8222   $58.82   $58.80   $58.80  
  Purchase #2 $208.76   11.122%   $231.9783   $231.98   $232.00   $232.00  
  Purchase #3 $244.86   11.787%   $273.7216   $273.72   $273.70   $273.70  
  Purchase #4 $48.92   13.467%   $55.5081   $55.51   $55.50   $55.50  
  Purchase #5 $128.68   3.729%   $133.4785   $133.48   $133.50   $133.50  
  Purchase #6 $241.58   10.444%   $266.8106   $266.81   $266.80   $266.80  
  Purchase #7 $15.91   11.432%   $17.7288   $17.73   $17.75   $17.70  
  7 purchase totals = $940.38       $1,038.0481   $1,038.05   $1,038.05   $1,038.00