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 $247.57   5.110%   $260.2208   $260.22   $260.20   $260.20  
  Purchase #2 $79.31   8.282%   $85.8785   $85.88   $85.90   $85.90  
  Purchase #3 $161.80   12.603%   $182.1917   $182.19   $182.20   $182.20  
  Purchase #4 $8.69   5.288%   $9.1495   $9.15   $9.15   $9.10  
  Purchase #5 $218.54   3.415%   $226.0031   $226.00   $226.00   $226.00  
  Purchase #6 $103.85   10.392%   $114.6421   $114.64   $114.65   $114.60  
  Purchase #7 $114.65   6.409%   $121.9979   $122.00   $122.00   $122.00  
  7 purchase totals = $934.41       $1,000.0836   $1,000.08   $1,000.10   $1,000.00