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 $223.64   12.459%   $251.5033   $251.50   $251.50   $251.50  
  Purchase #2 $57.67   13.415%   $65.4064   $65.41   $65.40   $65.40  
  Purchase #3 $183.81   4.297%   $191.7083   $191.71   $191.70   $191.70  
  Purchase #4 $13.97   3.231%   $14.4214   $14.42   $14.40   $14.40  
  Purchase #5 $87.60   12.254%   $98.3345   $98.33   $98.35   $98.30  
  Purchase #6 $240.40   9.273%   $262.6923   $262.69   $262.70   $262.70  
  Purchase #7 $136.55   11.299%   $151.9788   $151.98   $152.00   $152.00  
  7 purchase totals = $943.64       $1,036.0450   $1,036.04   $1,036.05   $1,036.00