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 $176.56   8.575%   $191.7   $191.70   $191.70   $191.70  
  Purchase #2 $13.27   7.199%   $14.2253   $14.23   $14.25   $14.20  
  Purchase #3 $9.46   4.151%   $9.8527   $9.85   $9.85   $9.90  
  Purchase #4 $242.98   9.170%   $265.2613   $265.26   $265.25   $265.30  
  Purchase #5 $83.83   11.802%   $93.7236   $93.72   $93.70   $93.70  
  Purchase #6 $183.86   11.125%   $204.3144   $204.31   $204.30   $204.30  
  Purchase #7 $173.44   5.813%   $183.5221   $183.52   $183.50   $183.50  
  7 purchase totals = $883.40       $962.5994   $962.59   $962.55   $962.60