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 $22.34   8.333%   $24.2016   $24.20   $24.20   $24.20  
  Purchase #2 $146.61   7.120%   $157.0486   $157.05   $157.05   $157.00  
  Purchase #3 $58.91   4.319%   $61.4543   $61.45   $61.45   $61.50  
  Purchase #4 $202.66   5.696%   $214.2035   $214.20   $214.20   $214.20  
  Purchase #5 $24.50   11.372%   $27.2861   $27.29   $27.30   $27.30  
  Purchase #6 $245.73   13.444%   $278.7659   $278.77   $278.75   $278.80  
  Purchase #7 $183.75   10.761%   $203.5233   $203.52   $203.50   $203.50  
  7 purchase totals = $884.50       $966.4833   $966.48   $966.45   $966.50