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 $22.77   6.499%   $24.2498   $24.25   $24.25   $24.20  
  Purchase #2 $63.30   13.444%   $71.8101   $71.81   $71.80   $71.80  
  Purchase #3 $59.76   13.272%   $67.6913   $67.69   $67.70   $67.70  
  Purchase #4 $28.33   9.575%   $31.0426   $31.04   $31.05   $31.00  
  Purchase #5 $218.73   9.357%   $239.1966   $239.20   $239.20   $239.20  
  Purchase #6 $250.29   5.580%   $264.2562   $264.26   $264.25   $264.30  
  Purchase #7 $56.60   9.498%   $61.9759   $61.98   $62.00   $62.00  
  7 purchase totals = $699.78       $760.2225   $760.23   $760.25   $760.20