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 $56.96   3.178%   $58.7702   $58.77   $58.75   $58.80  
  Purchase #2 $250.88   10.659%   $277.6213   $277.62   $277.60   $277.60  
  Purchase #3 $161.56   12.307%   $181.4432   $181.44   $181.45   $181.40  
  Purchase #4 $27.98   8.668%   $30.4053   $30.41   $30.40   $30.40  
  Purchase #5 $226.31   7.292%   $242.8125   $242.81   $242.80   $242.80  
  Purchase #6 $38.89   13.466%   $44.1269   $44.13   $44.15   $44.10  
  Purchase #7 $176.55   12.452%   $198.534   $198.53   $198.55   $198.50  
  7 purchase totals = $939.13       $1,033.7134   $1,033.71   $1,033.70   $1,033.60