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 $68.61   7.816%   $73.9726   $73.97   $73.95   $74.00  
  Purchase #2 $174.98   13.344%   $198.3293   $198.33   $198.35   $198.30  
  Purchase #3 $59.31   13.141%   $67.1039   $67.10   $67.10   $67.10  
  Purchase #4 $54.91   6.624%   $58.5472   $58.55   $58.55   $58.50  
  Purchase #5 $66.69   13.184%   $75.4824   $75.48   $75.50   $75.50  
  Purchase #6 $34.49   10.273%   $38.0332   $38.03   $38.05   $38.00  
  Purchase #7 $5.72   5.147%   $6.0144   $6.01   $6.00   $6.00  
  7 purchase totals = $464.71       $517.4830   $517.47   $517.50   $517.40