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 $214.46   12.624%   $241.5334   $241.53   $241.55   $241.50  
  Purchase #2 $154.73   7.519%   $166.3641   $166.36   $166.35   $166.40  
  Purchase #3 $170.88   6.438%   $181.8813   $181.88   $181.90   $181.90  
  Purchase #4 $171.26   9.165%   $186.956   $186.96   $186.95   $187.00  
  Purchase #5 $22.36   4.354%   $23.3336   $23.33   $23.35   $23.30  
  Purchase #6 $11.43   5.475%   $12.0558   $12.06   $12.05   $12.10  
  Purchase #7 $200.86   5.284%   $211.4734   $211.47   $211.45   $211.50  
  7 purchase totals = $945.98       $1,023.5976   $1,023.59   $1,023.60   $1,023.70