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 $118.95   6.109%   $126.2167   $126.22   $126.20   $126.20  
  Purchase #2 $67.52   13.862%   $76.8796   $76.88   $76.90   $76.90  
  Purchase #3 $192.93   7.233%   $206.8846   $206.88   $206.90   $206.90  
  Purchase #4 $135.91   3.202%   $140.2618   $140.26   $140.25   $140.30  
  Purchase #5 $135.39   11.157%   $150.4955   $150.50   $150.50   $150.50  
  Purchase #6 $73.77   7.506%   $79.3072   $79.31   $79.30   $79.30  
  Purchase #7 $216.88   11.524%   $241.8733   $241.87   $241.85   $241.90  
  7 purchase totals = $941.35       $1,021.9187   $1,021.92   $1,021.90   $1,022.00