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 $60.52   5.748%   $63.9987   $64.00   $64.00   $64.00  
  Purchase #2 $66.28   6.336%   $70.4795   $70.48   $70.50   $70.50  
  Purchase #3 $211.38   12.260%   $237.2952   $237.30   $237.30   $237.30  
  Purchase #4 $117.29   9.206%   $128.0877   $128.09   $128.10   $128.10  
  Purchase #5 $114.47   10.533%   $126.5271   $126.53   $126.55   $126.50  
  Purchase #6 $227.62   3.227%   $234.9653   $234.97   $234.95   $235.00  
  Purchase #7 $147.82   9.117%   $161.2967   $161.30   $161.30   $161.30  
  7 purchase totals = $945.38       $1,022.6502   $1,022.67   $1,022.70   $1,022.70