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 $182.60   13.340%   $206.9588   $206.96   $206.95   $207.00  
  Purchase #2 $239.33   4.495%   $250.0879   $250.09   $250.10   $250.10  
  Purchase #3 $39.51   8.513%   $42.8735   $42.87   $42.85   $42.90  
  Purchase #4 $24.79   10.616%   $27.4217   $27.42   $27.40   $27.40  
  Purchase #5 $14.84   12.708%   $16.7259   $16.73   $16.75   $16.70  
  Purchase #6 $211.76   7.804%   $228.2858   $228.29   $228.30   $228.30  
  Purchase #7 $11.59   6.122%   $12.2995   $12.30   $12.30   $12.30  
  7 purchase totals = $724.42       $784.6531   $784.66   $784.65   $784.70