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 $5.71   5.814%   $6.042   $6.04   $6.05   $6.00  
  Purchase #2 $233.61   11.570%   $260.6387   $260.64   $260.65   $260.60  
  Purchase #3 $156.41   11.233%   $173.9795   $173.98   $174.00   $174.00  
  Purchase #4 $99.66   6.162%   $105.801   $105.80   $105.80   $105.80  
  Purchase #5 $209.86   11.277%   $233.5259   $233.53   $233.55   $233.50  
  Purchase #6 $199.55   6.398%   $212.3172   $212.32   $212.30   $212.30  
  Purchase #7 $154.62   7.600%   $166.3711   $166.37   $166.35   $166.40  
  7 purchase totals = $1,059.42       $1,158.6754   $1,158.68   $1,158.70   $1,158.60