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 $59.49   7.688%   $64.0636   $64.06   $64.05   $64.10  
  Purchase #2 $172.90   6.612%   $184.3321   $184.33   $184.35   $184.30  
  Purchase #3 $154.89   6.841%   $165.486   $165.49   $165.50   $165.50  
  Purchase #4 $93.29   3.853%   $96.8845   $96.88   $96.90   $96.90  
  Purchase #5 $176.37   7.855%   $190.2239   $190.22   $190.20   $190.20  
  Purchase #6 $109.64   12.134%   $122.9437   $122.94   $122.95   $122.90  
  Purchase #7 $232.97   12.110%   $261.1827   $261.18   $261.20   $261.20  
  7 purchase totals = $999.55       $1,085.1165   $1,085.10   $1,085.15   $1,085.10