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 $61.69   8.537%   $66.9565   $66.96   $66.95   $67.00  
  Purchase #2 $16.38   10.656%   $18.1255   $18.13   $18.15   $18.10  
  Purchase #3 $212.57   6.601%   $226.6017   $226.60   $226.60   $226.60  
  Purchase #4 $227.51   3.307%   $235.0338   $235.03   $235.05   $235.00  
  Purchase #5 $9.96   12.732%   $11.2281   $11.23   $11.25   $11.20  
  Purchase #6 $161.33   6.108%   $171.184   $171.18   $171.20   $171.20  
  Purchase #7 $5.90   12.485%   $6.6366   $6.64   $6.65   $6.60  
  7 purchase totals = $695.34       $735.7662   $735.77   $735.85   $735.70