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 $206.79   4.740%   $216.5918   $216.59   $216.60   $216.60  
  Purchase #2 $58.97   13.651%   $67.02   $67.02   $67.00   $67.00  
  Purchase #3 $168.42   3.691%   $174.6364   $174.64   $174.65   $174.60  
  Purchase #4 $179.80   8.297%   $194.718   $194.72   $194.70   $194.70  
  Purchase #5 $87.76   8.279%   $95.0257   $95.03   $95.05   $95.00  
  Purchase #6 $32.43   9.829%   $35.6175   $35.62   $35.60   $35.60  
  Purchase #7 $67.89   12.549%   $76.4095   $76.41   $76.40   $76.40  
  7 purchase totals = $802.06       $860.0189   $860.03   $860.00   $859.90