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 $74.41   3.132%   $76.7405   $76.74   $76.75   $76.70  
  Purchase #2 $66.83   6.277%   $71.0249   $71.02   $71.00   $71.00  
  Purchase #3 $203.53   8.317%   $220.4576   $220.46   $220.45   $220.50  
  Purchase #4 $66.95   10.545%   $74.0099   $74.01   $74.00   $74.00  
  Purchase #5 $71.91   3.860%   $74.6857   $74.69   $74.70   $74.70  
  Purchase #6 $72.91   11.366%   $81.197   $81.20   $81.20   $81.20  
  Purchase #7 $246.47   10.268%   $271.7775   $271.78   $271.80   $271.80  
  7 purchase totals = $803.01       $869.8931   $869.90   $869.90   $869.90