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 $63.84   7.494%   $68.6242   $68.62   $68.60   $68.60  
  Purchase #2 $87.35   6.108%   $92.6853   $92.69   $92.70   $92.70  
  Purchase #3 $208.62   7.786%   $224.8632   $224.86   $224.85   $224.90  
  Purchase #4 $32.47   3.651%   $33.6555   $33.66   $33.65   $33.70  
  Purchase #5 $162.81   10.563%   $180.0076   $180.01   $180.00   $180.00  
  Purchase #6 $186.36   8.154%   $201.5558   $201.56   $201.55   $201.60  
  Purchase #7 $29.35   7.366%   $31.5119   $31.51   $31.50   $31.50  
  7 purchase totals = $770.80       $832.9035   $832.91   $832.85   $833.00