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 $53.67   11.867%   $60.039   $60.04   $60.05   $60.00  
  Purchase #2 $23.28   5.344%   $24.5241   $24.52   $24.50   $24.50  
  Purchase #3 $32.67   12.453%   $36.7384   $36.74   $36.75   $36.70  
  Purchase #4 $240.53   8.850%   $261.8169   $261.82   $261.80   $261.80  
  Purchase #5 $80.66   8.272%   $87.3322   $87.33   $87.35   $87.30  
  Purchase #6 $209.70   6.170%   $222.6385   $222.64   $222.65   $222.60  
  Purchase #7 $67.54   7.542%   $72.6339   $72.63   $72.65   $72.60  
  7 purchase totals = $708.05       $765.7230   $765.72   $765.75   $765.50