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 $76.77   10.455%   $84.7963   $84.80   $84.80   $84.80  
  Purchase #2 $101.96   10.831%   $113.0033   $113.00   $113.00   $113.00  
  Purchase #3 $226.91   10.790%   $251.3936   $251.39   $251.40   $251.40  
  Purchase #4 $237.35   7.463%   $255.0634   $255.06   $255.05   $255.10  
  Purchase #5 $31.76   9.172%   $34.673   $34.67   $34.65   $34.70  
  Purchase #6 $33.71   6.829%   $36.0121   $36.01   $36.00   $36.00  
  Purchase #7 $114.86   5.232%   $120.8695   $120.87   $120.85   $120.90  
  7 purchase totals = $823.32       $895.8112   $895.80   $895.75   $895.90