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 $61.42   13.414%   $69.6589   $69.66   $69.65   $69.70  
  Purchase #2 $234.96   13.642%   $267.0132   $267.01   $267.00   $267.00  
  Purchase #3 $80.47   3.759%   $83.4949   $83.49   $83.50   $83.50  
  Purchase #4 $104.74   3.183%   $108.0739   $108.07   $108.05   $108.10  
  Purchase #5 $157.29   5.103%   $165.3165   $165.32   $165.30   $165.30  
  Purchase #6 $72.48   13.443%   $82.2235   $82.22   $82.20   $82.20  
  Purchase #7 $205.64   13.747%   $233.9093   $233.91   $233.90   $233.90  
  7 purchase totals = $917.00       $1,009.6902   $1,009.68   $1,009.60   $1,009.70