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 $67.95   7.840%   $73.2773   $73.28   $73.30   $73.30  
  Purchase #2 $152.55   8.306%   $165.2208   $165.22   $165.20   $165.20  
  Purchase #3 $180.61   5.178%   $189.962   $189.96   $189.95   $190.00  
  Purchase #4 $220.36   3.740%   $228.6015   $228.60   $228.60   $228.60  
  Purchase #5 $82.62   3.139%   $85.2134   $85.21   $85.20   $85.20  
  Purchase #6 $38.86   10.577%   $42.9702   $42.97   $42.95   $43.00  
  Purchase #7 $247.51   11.579%   $276.1692   $276.17   $276.15   $276.20  
  7 purchase totals = $990.46       $1,061.4144   $1,061.41   $1,061.35   $1,061.50