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 $68.39   10.431%   $75.5238   $75.52   $75.50   $75.50  
  Purchase #2 $60.70   10.619%   $67.1457   $67.15   $67.15   $67.10  
  Purchase #3 $162.36   13.556%   $184.3695   $184.37   $184.35   $184.40  
  Purchase #4 $89.68   9.106%   $97.8463   $97.85   $97.85   $97.80  
  Purchase #5 $33.29   9.347%   $36.4016   $36.40   $36.40   $36.40  
  Purchase #6 $125.72   4.409%   $131.263   $131.26   $131.25   $131.30  
  Purchase #7 $237.78   5.147%   $250.0185   $250.02   $250.00   $250.00  
  7 purchase totals = $777.92       $842.5684   $842.57   $842.50   $842.50