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 $60.80   8.292%   $65.8415   $65.84   $65.85   $65.80  
  Purchase #2 $89.69   4.248%   $93.5   $93.50   $93.50   $93.50  
  Purchase #3 $96.31   12.512%   $108.3603   $108.36   $108.35   $108.40  
  Purchase #4 $98.29   7.257%   $105.4229   $105.42   $105.40   $105.40  
  Purchase #5 $196.47   11.568%   $219.1976   $219.20   $219.20   $219.20  
  Purchase #6 $226.54   8.447%   $245.6758   $245.68   $245.70   $245.70  
  Purchase #7 $24.75   6.253%   $26.2976   $26.30   $26.30   $26.30  
  7 purchase totals = $792.85       $864.2957   $864.30   $864.30   $864.30