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 $62.55   8.676%   $67.9768   $67.98   $68.00   $68.00  
  Purchase #2 $83.90   8.727%   $91.222   $91.22   $91.20   $91.20  
  Purchase #3 $108.42   5.864%   $114.7777   $114.78   $114.80   $114.80  
  Purchase #4 $244.84   4.384%   $255.5738   $255.57   $255.55   $255.60  
  Purchase #5 $171.60   9.255%   $187.4816   $187.48   $187.50   $187.50  
  Purchase #6 $49.56   8.321%   $53.6839   $53.68   $53.70   $53.70  
  Purchase #7 $48.42   9.182%   $52.8659   $52.87   $52.85   $52.90  
  7 purchase totals = $769.29       $823.5817   $823.58   $823.60   $823.70