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 $220.98   11.748%   $246.9407   $246.94   $246.95   $246.90  
  Purchase #2 $128.73   12.425%   $144.7247   $144.72   $144.70   $144.70  
  Purchase #3 $147.27   12.854%   $166.2001   $166.20   $166.20   $166.20  
  Purchase #4 $246.83   10.468%   $272.6682   $272.67   $272.65   $272.70  
  Purchase #5 $165.54   4.828%   $173.5323   $173.53   $173.55   $173.50  
  Purchase #6 $152.45   8.301%   $165.1049   $165.10   $165.10   $165.10  
  Purchase #7 $27.53   5.626%   $29.0788   $29.08   $29.10   $29.10  
  7 purchase totals = $1,089.33       $1,198.2497   $1,198.24   $1,198.25   $1,198.20