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 $183.98   5.138%   $193.4329   $193.43   $193.45   $193.40  
  Purchase #2 $71.84   13.835%   $81.7791   $81.78   $81.80   $81.80  
  Purchase #3 $93.71   4.783%   $98.1921   $98.19   $98.20   $98.20  
  Purchase #4 $144.31   8.190%   $156.129   $156.13   $156.15   $156.10  
  Purchase #5 $120.50   9.737%   $132.2331   $132.23   $132.25   $132.20  
  Purchase #6 $49.62   12.147%   $55.6473   $55.65   $55.65   $55.60  
  Purchase #7 $40.27   8.111%   $43.5363   $43.54   $43.55   $43.50  
  7 purchase totals = $704.23       $760.9498   $760.95   $761.05   $760.80