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 $58.65   4.611%   $61.3544   $61.35   $61.35   $61.40  
  Purchase #2 $17.61   3.842%   $18.2866   $18.29   $18.30   $18.30  
  Purchase #3 $89.84   13.127%   $101.6333   $101.63   $101.65   $101.60  
  Purchase #4 $105.93   12.333%   $118.9943   $118.99   $119.00   $119.00  
  Purchase #5 $231.41   6.244%   $245.8592   $245.86   $245.85   $245.90  
  Purchase #6 $237.74   11.261%   $264.5119   $264.51   $264.50   $264.50  
  Purchase #7 $230.28   9.725%   $252.6747   $252.67   $252.65   $252.70  
  7 purchase totals = $971.46       $1,063.3144   $1,063.30   $1,063.30   $1,063.40