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 $184.46   6.208%   $195.9113   $195.91   $195.90   $195.90  
  Purchase #2 $228.78   12.789%   $258.0387   $258.04   $258.05   $258.00  
  Purchase #3 $81.50   6.444%   $86.7519   $86.75   $86.75   $86.80  
  Purchase #4 $116.47   3.556%   $120.6117   $120.61   $120.60   $120.60  
  Purchase #5 $119.58   10.600%   $132.2555   $132.26   $132.25   $132.30  
  Purchase #6 $225.67   8.360%   $244.536   $244.54   $244.55   $244.50  
  Purchase #7 $33.40   8.646%   $36.2878   $36.29   $36.30   $36.30  
  7 purchase totals = $989.86       $1,074.3929   $1,074.40   $1,074.40   $1,074.40