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 $54.40   10.132%   $59.9118   $59.91   $59.90   $59.90  
  Purchase #2 $82.44   12.133%   $92.4424   $92.44   $92.45   $92.40  
  Purchase #3 $98.93   13.555%   $112.34   $112.34   $112.35   $112.30  
  Purchase #4 $178.94   8.373%   $193.9226   $193.92   $193.90   $193.90  
  Purchase #5 $216.80   6.365%   $230.5993   $230.60   $230.60   $230.60  
  Purchase #6 $92.55   5.186%   $97.3496   $97.35   $97.35   $97.30  
  Purchase #7 $102.83   3.538%   $106.4681   $106.47   $106.45   $106.50  
  7 purchase totals = $826.89       $893.0338   $893.03   $893.00   $892.90