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 $187.26   8.306%   $202.8138   $202.81   $202.80   $202.80  
  Purchase #2 $61.38   8.563%   $66.636   $66.64   $66.65   $66.60  
  Purchase #3 $69.34   3.493%   $71.762   $71.76   $71.75   $71.80  
  Purchase #4 $120.50   7.308%   $129.3061   $129.31   $129.30   $129.30  
  Purchase #5 $82.67   8.362%   $89.5829   $89.58   $89.60   $89.60  
  Purchase #6 $236.89   13.535%   $268.9531   $268.95   $268.95   $269.00  
  Purchase #7 $121.53   8.261%   $131.5696   $131.57   $131.55   $131.60  
  7 purchase totals = $879.57       $960.6235   $960.62   $960.60   $960.70