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 $69.75   6.705%   $74.4267   $74.43   $74.45   $74.40  
  Purchase #2 $200.87   4.436%   $209.7806   $209.78   $209.80   $209.80  
  Purchase #3 $197.43   7.843%   $212.9144   $212.91   $212.90   $212.90  
  Purchase #4 $183.37   5.281%   $193.0538   $193.05   $193.05   $193.10  
  Purchase #5 $85.87   13.566%   $97.5191   $97.52   $97.50   $97.50  
  Purchase #6 $234.61   12.307%   $263.4835   $263.48   $263.50   $263.50  
  Purchase #7 $232.90   3.684%   $241.48   $241.48   $241.50   $241.50  
  7 purchase totals = $1,204.80       $1,292.6581   $1,292.65   $1,292.70   $1,292.70