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 $207.57   12.355%   $233.2153   $233.22   $233.20   $233.20  
  Purchase #2 $245.90   7.165%   $263.5187   $263.52   $263.50   $263.50  
  Purchase #3 $76.52   11.404%   $85.2463   $85.25   $85.25   $85.20  
  Purchase #4 $202.38   7.154%   $216.8583   $216.86   $216.85   $216.90  
  Purchase #5 $230.57   8.533%   $250.2445   $250.24   $250.25   $250.20  
  Purchase #6 $242.97   10.170%   $267.68   $267.68   $267.70   $267.70  
  Purchase #7 $172.81   3.681%   $179.1711   $179.17   $179.15   $179.20  
  7 purchase totals = $1,378.72       $1,495.9342   $1,495.94   $1,495.90   $1,495.90