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 $158.55   5.333%   $167.0055   $167.01   $167.00   $167.00  
  Purchase #2 $216.44   4.643%   $226.4893   $226.49   $226.50   $226.50  
  Purchase #3 $221.63   6.233%   $235.4442   $235.44   $235.45   $235.40  
  Purchase #4 $58.87   3.641%   $61.0135   $61.01   $61.00   $61.00  
  Purchase #5 $209.71   6.330%   $222.9846   $222.98   $223.00   $223.00  
  Purchase #6 $163.72   7.721%   $176.3608   $176.36   $176.35   $176.40  
  Purchase #7 $250.82   12.872%   $283.1056   $283.11   $283.10   $283.10  
  7 purchase totals = $1,279.74       $1,372.4035   $1,372.40   $1,372.40   $1,372.40