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 $68.81   11.151%   $76.483   $76.48   $76.50   $76.50  
  Purchase #2 $96.63   4.847%   $101.3137   $101.31   $101.30   $101.30  
  Purchase #3 $166.46   5.637%   $175.8434   $175.84   $175.85   $175.80  
  Purchase #4 $205.52   5.268%   $216.3468   $216.35   $216.35   $216.30  
  Purchase #5 $31.66   10.252%   $34.9058   $34.91   $34.90   $34.90  
  Purchase #6 $165.42   4.584%   $173.0029   $173.00   $173.00   $173.00  
  Purchase #7 $226.36   11.443%   $252.2624   $252.26   $252.25   $252.30  
  7 purchase totals = $960.86       $1,030.1580   $1,030.15   $1,030.15   $1,030.10