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 $129.86   12.397%   $145.9587   $145.96   $145.95   $146.00  
  Purchase #2 $236.87   7.241%   $254.0218   $254.02   $254.00   $254.00  
  Purchase #3 $250.54   7.683%   $269.789   $269.79   $269.80   $269.80  
  Purchase #4 $239.64   9.868%   $263.2877   $263.29   $263.30   $263.30  
  Purchase #5 $128.75   3.151%   $132.8069   $132.81   $132.80   $132.80  
  Purchase #6 $194.47   9.641%   $213.2189   $213.22   $213.20   $213.20  
  Purchase #7 $162.76   12.141%   $182.5207   $182.52   $182.50   $182.50  
  7 purchase totals = $1,342.89       $1,461.6037   $1,461.61   $1,461.55   $1,461.60