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 $50.67   11.453%   $56.4732   $56.47   $56.45   $56.50  
  Purchase #2 $207.31   4.685%   $217.0225   $217.02   $217.00   $217.00  
  Purchase #3 $223.56   3.583%   $231.5702   $231.57   $231.55   $231.60  
  Purchase #4 $59.48   12.566%   $66.9543   $66.95   $66.95   $67.00  
  Purchase #5 $191.74   8.813%   $208.638   $208.64   $208.65   $208.60  
  Purchase #6 $166.37   13.485%   $188.805   $188.81   $188.80   $188.80  
  Purchase #7 $203.36   9.708%   $223.1022   $223.10   $223.10   $223.10  
  7 purchase totals = $1,102.49       $1,192.5654   $1,192.56   $1,192.50   $1,192.60