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 $50.65   13.129%   $57.2998   $57.30   $57.30   $57.30  
  Purchase #2 $232.98   3.640%   $241.4605   $241.46   $241.45   $241.50  
  Purchase #3 $70.97   9.245%   $77.5312   $77.53   $77.55   $77.50  
  Purchase #4 $223.55   9.358%   $244.4698   $244.47   $244.45   $244.50  
  Purchase #5 $38.70   3.432%   $40.0282   $40.03   $40.05   $40.00  
  Purchase #6 $160.69   10.849%   $178.1233   $178.12   $178.10   $178.10  
  Purchase #7 $198.74   9.501%   $217.6223   $217.62   $217.60   $217.60  
  7 purchase totals = $976.28       $1,056.5351   $1,056.53   $1,056.50   $1,056.50