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 $75.93   9.591%   $83.2124   $83.21   $83.20   $83.20  
  Purchase #2 $54.39   12.618%   $61.2529   $61.25   $61.25   $61.30  
  Purchase #3 $187.35   6.104%   $198.7858   $198.79   $198.80   $198.80  
  Purchase #4 $115.40   9.579%   $126.4542   $126.45   $126.45   $126.50  
  Purchase #5 $175.46   8.614%   $190.5741   $190.57   $190.55   $190.60  
  Purchase #6 $228.95   9.619%   $250.9727   $250.97   $250.95   $251.00  
  Purchase #7 $87.30   8.432%   $94.6611   $94.66   $94.65   $94.70  
  7 purchase totals = $924.78       $1,005.9132   $1,005.90   $1,005.85   $1,006.10