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 $250.92   6.744%   $267.842   $267.84   $267.85   $267.80  
  Purchase #2 $113.68   9.480%   $124.4569   $124.46   $124.45   $124.50  
  Purchase #3 $55.29   13.374%   $62.6845   $62.68   $62.70   $62.70  
  Purchase #4 $113.96   10.227%   $125.6147   $125.61   $125.60   $125.60  
  Purchase #5 $158.85   5.340%   $167.3326   $167.33   $167.35   $167.30  
  Purchase #6 $242.45   8.453%   $262.9443   $262.94   $262.95   $262.90  
  Purchase #7 $201.94   10.577%   $223.2992   $223.30   $223.30   $223.30  
  7 purchase totals = $1,137.09       $1,234.1742   $1,234.16   $1,234.20   $1,234.10