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 $191.74   12.845%   $216.369   $216.37   $216.35   $216.40  
  Purchase #2 $57.36   4.531%   $59.959   $59.96   $59.95   $60.00  
  Purchase #3 $168.36   7.646%   $181.2328   $181.23   $181.25   $181.20  
  Purchase #4 $144.95   12.269%   $162.7339   $162.73   $162.75   $162.70  
  Purchase #5 $242.68   3.562%   $251.3243   $251.32   $251.30   $251.30  
  Purchase #6 $168.46   5.406%   $177.5669   $177.57   $177.55   $177.60  
  Purchase #7 $118.98   11.292%   $132.4152   $132.42   $132.40   $132.40  
  7 purchase totals = $1,092.53       $1,181.6011   $1,181.60   $1,181.55   $1,181.60