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 $103.97   11.113%   $115.5242   $115.52   $115.50   $115.50  
  Purchase #2 $145.36   5.697%   $153.6412   $153.64   $153.65   $153.60  
  Purchase #3 $36.56   13.401%   $41.4594   $41.46   $41.45   $41.50  
  Purchase #4 $173.41   3.620%   $179.6874   $179.69   $179.70   $179.70  
  Purchase #5 $207.65   7.692%   $223.6224   $223.62   $223.60   $223.60  
  Purchase #6 $14.84   13.422%   $16.8318   $16.83   $16.85   $16.80  
  Purchase #7 $101.66   7.420%   $109.2032   $109.20   $109.20   $109.20  
  7 purchase totals = $783.45       $839.9696   $839.96   $839.95   $839.90