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 $180.50   8.506%   $195.8533   $195.85   $195.85   $195.90  
  Purchase #2 $44.90   10.810%   $49.7537   $49.75   $49.75   $49.80  
  Purchase #3 $71.49   4.615%   $74.7893   $74.79   $74.80   $74.80  
  Purchase #4 $14.72   4.124%   $15.3271   $15.33   $15.35   $15.30  
  Purchase #5 $212.26   13.164%   $240.2019   $240.20   $240.20   $240.20  
  Purchase #6 $243.46   7.218%   $261.0329   $261.03   $261.05   $261.00  
  Purchase #7 $85.88   9.488%   $94.0283   $94.03   $94.05   $94.00  
  7 purchase totals = $853.21       $930.9865   $930.98   $931.05   $931.00