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 $194.32   9.650%   $213.0719   $213.07   $213.05   $213.10  
  Purchase #2 $239.66   4.736%   $251.0103   $251.01   $251.00   $251.00  
  Purchase #3 $117.51   6.168%   $124.758   $124.76   $124.75   $124.80  
  Purchase #4 $9.74   5.742%   $10.2993   $10.30   $10.30   $10.30  
  Purchase #5 $220.59   11.378%   $245.6887   $245.69   $245.70   $245.70  
  Purchase #6 $216.68   6.336%   $230.4088   $230.41   $230.40   $230.40  
  Purchase #7 $152.77   5.390%   $161.0043   $161.00   $161.00   $161.00  
  7 purchase totals = $1,151.27       $1,236.2413   $1,236.24   $1,236.20   $1,236.30