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 $192.36   6.519%   $204.8999   $204.90   $204.90   $204.90  
  Purchase #2 $102.69   10.538%   $113.5115   $113.51   $113.50   $113.50  
  Purchase #3 $69.75   6.434%   $74.2377   $74.24   $74.25   $74.20  
  Purchase #4 $130.38   6.361%   $138.6735   $138.67   $138.65   $138.70  
  Purchase #5 $105.59   12.379%   $118.661   $118.66   $118.65   $118.70  
  Purchase #6 $122.74   6.403%   $130.599   $130.60   $130.60   $130.60  
  Purchase #7 $212.30   10.225%   $234.0077   $234.01   $234.00   $234.00  
  7 purchase totals = $935.81       $1,014.5903   $1,014.59   $1,014.55   $1,014.60