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 $177.49   6.468%   $188.9701   $188.97   $188.95   $189.00  
  Purchase #2 $97.39   9.510%   $106.6518   $106.65   $106.65   $106.70  
  Purchase #3 $74.75   9.731%   $82.0239   $82.02   $82.00   $82.00  
  Purchase #4 $242.99   4.113%   $252.9842   $252.98   $253.00   $253.00  
  Purchase #5 $170.97   12.285%   $191.9737   $191.97   $191.95   $192.00  
  Purchase #6 $235.90   3.676%   $244.5717   $244.57   $244.55   $244.60  
  Purchase #7 $122.46   4.863%   $128.4152   $128.42   $128.40   $128.40  
  7 purchase totals = $1,121.95       $1,195.5906   $1,195.58   $1,195.50   $1,195.70