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 $59.53   3.380%   $61.5421   $61.54   $61.55   $61.50  
  Purchase #2 $230.93   7.830%   $249.0118   $249.01   $249.00   $249.00  
  Purchase #3 $214.81   9.687%   $235.6186   $235.62   $235.60   $235.60  
  Purchase #4 $159.97   12.585%   $180.1022   $180.10   $180.10   $180.10  
  Purchase #5 $11.76   9.108%   $12.8311   $12.83   $12.85   $12.80  
  Purchase #6 $25.93   9.812%   $28.4743   $28.47   $28.45   $28.50  
  Purchase #7 $214.44   8.607%   $232.8969   $232.90   $232.90   $232.90  
  7 purchase totals = $917.37       $1,000.4770   $1,000.47   $1,000.45   $1,000.40