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 $194.68   10.854%   $215.8106   $215.81   $215.80   $215.80  
  Purchase #2 $183.92   6.391%   $195.6743   $195.67   $195.65   $195.70  
  Purchase #3 $195.33   4.384%   $203.8933   $203.89   $203.90   $203.90  
  Purchase #4 $76.32   10.759%   $84.5313   $84.53   $84.55   $84.50  
  Purchase #5 $119.42   4.504%   $124.7987   $124.80   $124.80   $124.80  
  Purchase #6 $111.84   8.264%   $121.0825   $121.08   $121.10   $121.10  
  Purchase #7 $64.52   5.273%   $67.9221   $67.92   $67.90   $67.90  
  7 purchase totals = $946.03       $1,013.7128   $1,013.70   $1,013.70   $1,013.70