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 $96.94   6.420%   $103.1635   $103.16   $103.15   $103.20  
  Purchase #2 $238.33   6.308%   $253.3639   $253.36   $253.35   $253.40  
  Purchase #3 $248.46   11.679%   $277.4776   $277.48   $277.50   $277.50  
  Purchase #4 $26.92   6.755%   $28.7384   $28.74   $28.75   $28.70  
  Purchase #5 $183.65   5.864%   $194.4192   $194.42   $194.40   $194.40  
  Purchase #6 $235.44   13.644%   $267.5634   $267.56   $267.55   $267.60  
  Purchase #7 $67.67   7.590%   $72.8062   $72.81   $72.80   $72.80  
  7 purchase totals = $1,097.41       $1,197.5322   $1,197.53   $1,197.50   $1,197.60