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 $213.52   12.198%   $239.5652   $239.57   $239.55   $239.60  
  Purchase #2 $177.45   9.514%   $194.3326   $194.33   $194.35   $194.30  
  Purchase #3 $117.49   13.750%   $133.6449   $133.64   $133.65   $133.60  
  Purchase #4 $228.65   6.296%   $243.0458   $243.05   $243.05   $243.00  
  Purchase #5 $69.42   12.501%   $78.0982   $78.10   $78.10   $78.10  
  Purchase #6 $89.61   9.655%   $98.2618   $98.26   $98.25   $98.30  
  Purchase #7 $60.85   7.841%   $65.6212   $65.62   $65.60   $65.60  
  7 purchase totals = $956.99       $1,052.5697   $1,052.57   $1,052.55   $1,052.50