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 $84.26   11.113%   $93.6238   $93.62   $93.60   $93.60  
  Purchase #2 $98.53   6.833%   $105.2626   $105.26   $105.25   $105.30  
  Purchase #3 $164.95   9.593%   $180.7737   $180.77   $180.75   $180.80  
  Purchase #4 $240.77   6.536%   $256.5067   $256.51   $256.50   $256.50  
  Purchase #5 $225.97   7.262%   $242.3799   $242.38   $242.40   $242.40  
  Purchase #6 $183.79   10.178%   $202.4961   $202.50   $202.50   $202.50  
  Purchase #7 $71.57   4.550%   $74.8264   $74.83   $74.85   $74.80  
  7 purchase totals = $1,069.84       $1,155.8692   $1,155.87   $1,155.85   $1,155.90