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 $66.27   8.546%   $71.9334   $71.93   $71.95   $71.90  
  Purchase #2 $101.80   13.626%   $115.6713   $115.67   $115.65   $115.70  
  Purchase #3 $13.70   13.337%   $15.5272   $15.53   $15.55   $15.50  
  Purchase #4 $166.47   11.646%   $185.8571   $185.86   $185.85   $185.90  
  Purchase #5 $218.25   5.627%   $230.5309   $230.53   $230.55   $230.50  
  Purchase #6 $148.44   12.814%   $167.4611   $167.46   $167.45   $167.50  
  Purchase #7 $226.46   13.508%   $257.0502   $257.05   $257.05   $257.10  
  7 purchase totals = $941.39       $1,044.0312   $1,044.03   $1,044.05   $1,044.10