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 $118.77   6.274%   $126.2216   $126.22   $126.20   $126.20  
  Purchase #2 $73.98   12.695%   $83.3718   $83.37   $83.35   $83.40  
  Purchase #3 $153.53   10.114%   $169.058   $169.06   $169.05   $169.10  
  Purchase #4 $207.81   3.869%   $215.8502   $215.85   $215.85   $215.90  
  Purchase #5 $147.83   9.109%   $161.2958   $161.30   $161.30   $161.30  
  Purchase #6 $239.44   10.119%   $263.6689   $263.67   $263.65   $263.70  
  Purchase #7 $191.80   7.441%   $206.0718   $206.07   $206.05   $206.10  
  7 purchase totals = $1,133.16       $1,225.5381   $1,225.54   $1,225.45   $1,225.70