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 $59.78   4.686%   $62.5813   $62.58   $62.60   $62.60  
  Purchase #2 $197.79   13.632%   $224.7527   $224.75   $224.75   $224.80  
  Purchase #3 $176.28   8.823%   $191.8332   $191.83   $191.85   $191.80  
  Purchase #4 $130.44   6.275%   $138.6251   $138.63   $138.65   $138.60  
  Purchase #5 $240.64   9.156%   $262.673   $262.67   $262.65   $262.70  
  Purchase #6 $143.65   6.222%   $152.5879   $152.59   $152.60   $152.60  
  Purchase #7 $43.43   6.477%   $46.243   $46.24   $46.25   $46.20  
  7 purchase totals = $992.01       $1,079.2962   $1,079.29   $1,079.35   $1,079.30