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 $147.88   7.592%   $159.107   $159.11   $159.10   $159.10  
  Purchase #2 $195.68   11.351%   $217.8916   $217.89   $217.90   $217.90  
  Purchase #3 $115.40   4.497%   $120.5895   $120.59   $120.60   $120.60  
  Purchase #4 $68.74   10.854%   $76.201   $76.20   $76.20   $76.20  
  Purchase #5 $157.80   3.771%   $163.7506   $163.75   $163.75   $163.80  
  Purchase #6 $126.76   7.873%   $136.7398   $136.74   $136.75   $136.70  
  Purchase #7 $121.52   8.591%   $131.9598   $131.96   $131.95   $132.00  
  7 purchase totals = $933.78       $1,006.2393   $1,006.24   $1,006.25   $1,006.30