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 $60.79   6.362%   $64.6575   $64.66   $64.65   $64.70  
  Purchase #2 $181.42   11.867%   $202.9491   $202.95   $202.95   $202.90  
  Purchase #3 $106.72   12.530%   $120.092   $120.09   $120.10   $120.10  
  Purchase #4 $145.73   6.552%   $155.2782   $155.28   $155.30   $155.30  
  Purchase #5 $48.67   13.451%   $55.2166   $55.22   $55.20   $55.20  
  Purchase #6 $146.66   11.578%   $163.6403   $163.64   $163.65   $163.60  
  Purchase #7 $61.40   10.704%   $67.9723   $67.97   $67.95   $68.00  
  7 purchase totals = $751.39       $829.8060   $829.81   $829.80   $829.80