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 $60.82   4.665%   $63.6573   $63.66   $63.65   $63.70  
  Purchase #2 $214.38   12.303%   $240.7552   $240.76   $240.75   $240.80  
  Purchase #3 $232.49   5.592%   $245.4908   $245.49   $245.50   $245.50  
  Purchase #4 $126.60   9.363%   $138.4536   $138.45   $138.45   $138.50  
  Purchase #5 $69.25   5.754%   $73.2346   $73.23   $73.25   $73.20  
  Purchase #6 $11.81   10.760%   $13.0808   $13.08   $13.10   $13.10  
  Purchase #7 $93.41   12.572%   $105.1535   $105.15   $105.15   $105.20  
  7 purchase totals = $808.76       $879.8258   $879.82   $879.85   $880.00