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 $158.44   11.265%   $176.2883   $176.29   $176.30   $176.30  
  Purchase #2 $213.64   11.839%   $238.9328   $238.93   $238.95   $238.90  
  Purchase #3 $29.62   9.310%   $32.3776   $32.38   $32.40   $32.40  
  Purchase #4 $194.28   10.351%   $214.3899   $214.39   $214.40   $214.40  
  Purchase #5 $98.84   6.193%   $104.9612   $104.96   $104.95   $105.00  
  Purchase #6 $194.28   6.843%   $207.5746   $207.57   $207.55   $207.60  
  Purchase #7 $35.65   3.421%   $36.8696   $36.87   $36.85   $36.90  
  7 purchase totals = $924.75       $1,011.3940   $1,011.39   $1,011.40   $1,011.50