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 $61.42   4.596%   $64.2429   $64.24   $64.25   $64.20  
  Purchase #2 $227.66   8.255%   $246.4533   $246.45   $246.45   $246.50  
  Purchase #3 $206.69   6.371%   $219.8582   $219.86   $219.85   $219.90  
  Purchase #4 $92.26   3.350%   $95.3507   $95.35   $95.35   $95.40  
  Purchase #5 $161.62   5.835%   $171.0505   $171.05   $171.05   $171.10  
  Purchase #6 $56.61   5.842%   $59.9172   $59.92   $59.90   $59.90  
  Purchase #7 $160.60   4.511%   $167.8447   $167.84   $167.85   $167.80  
  7 purchase totals = $966.86       $1,024.7175   $1,024.71   $1,024.70   $1,024.80