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 $224.60   10.256%   $247.635   $247.64   $247.65   $247.60  
  Purchase #2 $104.98   11.817%   $117.3855   $117.39   $117.40   $117.40  
  Purchase #3 $160.78   10.635%   $177.879   $177.88   $177.90   $177.90  
  Purchase #4 $250.36   8.683%   $272.0988   $272.10   $272.10   $272.10  
  Purchase #5 $49.57   11.562%   $55.3013   $55.30   $55.30   $55.30  
  Purchase #6 $73.76   12.607%   $83.0589   $83.06   $83.05   $83.10  
  Purchase #7 $41.96   11.144%   $46.636   $46.64   $46.65   $46.60  
  7 purchase totals = $906.01       $999.9945   $1,000.01   $1,000.05   $1,000.00