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 $144.32   6.840%   $154.1915   $154.19   $154.20   $154.20  
  Purchase #2 $227.99   5.825%   $241.2704   $241.27   $241.25   $241.30  
  Purchase #3 $92.26   11.455%   $102.8284   $102.83   $102.85   $102.80  
  Purchase #4 $202.84   8.767%   $220.623   $220.62   $220.60   $220.60  
  Purchase #5 $61.58   13.219%   $69.7203   $69.72   $69.70   $69.70  
  Purchase #6 $241.84   11.184%   $268.8874   $268.89   $268.90   $268.90  
  Purchase #7 $90.50   5.326%   $95.32   $95.32   $95.30   $95.30  
  7 purchase totals = $1,061.33       $1,152.8410   $1,152.84   $1,152.80   $1,152.80