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 $136.57   5.220%   $143.699   $143.70   $143.70   $143.70  
  Purchase #2 $24.58   5.362%   $25.898   $25.90   $25.90   $25.90  
  Purchase #3 $214.66   4.718%   $224.7877   $224.79   $224.80   $224.80  
  Purchase #4 $148.72   12.603%   $167.4632   $167.46   $167.45   $167.50  
  Purchase #5 $197.37   9.323%   $215.7708   $215.77   $215.75   $215.80  
  Purchase #6 $51.77   12.510%   $58.2464   $58.25   $58.25   $58.20  
  Purchase #7 $143.92   10.237%   $158.6531   $158.65   $158.65   $158.70  
  7 purchase totals = $917.59       $994.5182   $994.52   $994.50   $994.60