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 $91.52   6.668%   $97.6226   $97.62   $97.60   $97.60  
  Purchase #2 $205.87   4.398%   $214.9242   $214.92   $214.90   $214.90  
  Purchase #3 $35.96   6.841%   $38.42   $38.42   $38.40   $38.40  
  Purchase #4 $36.53   8.389%   $39.5945   $39.59   $39.60   $39.60  
  Purchase #5 $110.29   9.488%   $120.7543   $120.75   $120.75   $120.80  
  Purchase #6 $181.48   6.370%   $193.0403   $193.04   $193.05   $193.00  
  Purchase #7 $10.70   10.439%   $11.817   $11.82   $11.80   $11.80  
  7 purchase totals = $672.35       $716.1729   $716.16   $716.10   $716.10