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 $178.25   3.236%   $184.0182   $184.02   $184.00   $184.00  
  Purchase #2 $60.42   3.232%   $62.3728   $62.37   $62.35   $62.40  
  Purchase #3 $209.70   5.579%   $221.3992   $221.40   $221.40   $221.40  
  Purchase #4 $186.39   8.307%   $201.8734   $201.87   $201.85   $201.90  
  Purchase #5 $40.56   10.147%   $44.6756   $44.68   $44.70   $44.70  
  Purchase #6 $243.63   9.739%   $267.3571   $267.36   $267.35   $267.40  
  Purchase #7 $35.97   4.530%   $37.5994   $37.60   $37.60   $37.60  
  7 purchase totals = $954.92       $1,019.2957   $1,019.30   $1,019.25   $1,019.40