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 $232.74   9.424%   $254.6734   $254.67   $254.65   $254.70  
  Purchase #2 $28.86   3.235%   $29.7936   $29.79   $29.80   $29.80  
  Purchase #3 $96.45   3.308%   $99.6406   $99.64   $99.65   $99.60  
  Purchase #4 $24.86   7.816%   $26.8031   $26.80   $26.80   $26.80  
  Purchase #5 $199.71   4.789%   $209.2741   $209.27   $209.25   $209.30  
  Purchase #6 $5.88   12.443%   $6.6116   $6.61   $6.60   $6.60  
  Purchase #7 $214.26   11.712%   $239.3541   $239.35   $239.35   $239.40  
  7 purchase totals = $802.76       $866.1505   $866.13   $866.10   $866.20