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 $238.52   12.306%   $267.8723   $267.87   $267.85   $267.90  
  Purchase #2 $117.67   12.133%   $131.9469   $131.95   $131.95   $131.90  
  Purchase #3 $236.86   4.418%   $247.3245   $247.32   $247.30   $247.30  
  Purchase #4 $86.32   5.862%   $91.3801   $91.38   $91.40   $91.40  
  Purchase #5 $229.65   4.191%   $239.2746   $239.27   $239.25   $239.30  
  Purchase #6 $147.40   8.752%   $160.3004   $160.30   $160.30   $160.30  
  Purchase #7 $207.52   12.623%   $233.7152   $233.72   $233.70   $233.70  
  7 purchase totals = $1,263.94       $1,371.8140   $1,371.81   $1,371.75   $1,371.80