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 $88.80   8.332%   $96.1988   $96.20   $96.20   $96.20  
  Purchase #2 $116.93   6.347%   $124.3515   $124.35   $124.35   $124.40  
  Purchase #3 $68.74   12.493%   $77.3277   $77.33   $77.35   $77.30  
  Purchase #4 $12.29   3.189%   $12.6819   $12.68   $12.70   $12.70  
  Purchase #5 $227.61   7.802%   $245.3681   $245.37   $245.35   $245.40  
  Purchase #6 $209.54   4.689%   $219.3653   $219.37   $219.35   $219.40  
  Purchase #7 $51.77   11.179%   $57.5574   $57.56   $57.55   $57.60  
  7 purchase totals = $775.68       $832.8507   $832.86   $832.85   $833.00