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 $74.91   11.463%   $83.4969   $83.50   $83.50   $83.50  
  Purchase #2 $194.78   8.803%   $211.9265   $211.93   $211.95   $211.90  
  Purchase #3 $23.76   8.120%   $25.6893   $25.69   $25.70   $25.70  
  Purchase #4 $233.62   13.623%   $265.4461   $265.45   $265.45   $265.40  
  Purchase #5 $199.38   6.102%   $211.5462   $211.55   $211.55   $211.50  
  Purchase #6 $173.68   6.755%   $185.4121   $185.41   $185.40   $185.40  
  Purchase #7 $83.25   5.131%   $87.5216   $87.52   $87.50   $87.50  
  7 purchase totals = $983.38       $1,071.0387   $1,071.05   $1,071.05   $1,070.90