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 $67.36   7.802%   $72.6154   $72.62   $72.60   $72.60  
  Purchase #2 $235.58   4.824%   $246.9444   $246.94   $246.95   $246.90  
  Purchase #3 $37.87   5.601%   $39.9911   $39.99   $40.00   $40.00  
  Purchase #4 $26.59   12.658%   $29.9558   $29.96   $29.95   $30.00  
  Purchase #5 $60.48   4.795%   $63.38   $63.38   $63.40   $63.40  
  Purchase #6 $145.50   12.118%   $163.1317   $163.13   $163.15   $163.10  
  Purchase #7 $165.75   12.855%   $187.0572   $187.06   $187.05   $187.10  
  7 purchase totals = $739.13       $803.0756   $803.08   $803.10   $803.10