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 $136.53   11.324%   $151.9907   $151.99   $152.00   $152.00  
  Purchase #2 $148.51   4.320%   $154.9256   $154.93   $154.95   $154.90  
  Purchase #3 $61.30   6.309%   $65.1674   $65.17   $65.15   $65.20  
  Purchase #4 $48.56   5.571%   $51.2653   $51.27   $51.25   $51.30  
  Purchase #5 $56.99   6.322%   $60.5929   $60.59   $60.60   $60.60  
  Purchase #6 $76.80   5.417%   $80.9603   $80.96   $80.95   $81.00  
  Purchase #7 $174.97   5.147%   $183.9757   $183.98   $184.00   $184.00  
  7 purchase totals = $703.66       $748.8779   $748.89   $748.90   $749.00