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 $60.90   10.441%   $67.2586   $67.26   $67.25   $67.30  
  Purchase #2 $215.84   4.761%   $226.1161   $226.12   $226.10   $226.10  
  Purchase #3 $124.85   5.726%   $131.9989   $132.00   $132.00   $132.00  
  Purchase #4 $9.99   7.526%   $10.7418   $10.74   $10.75   $10.70  
  Purchase #5 $117.89   10.797%   $130.6186   $130.62   $130.60   $130.60  
  Purchase #6 $216.27   6.624%   $230.5957   $230.60   $230.60   $230.60  
  Purchase #7 $211.93   13.616%   $240.7864   $240.79   $240.80   $240.80  
  7 purchase totals = $957.67       $1,038.1161   $1,038.13   $1,038.10   $1,038.10