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 $126.77   7.245%   $135.9545   $135.95   $135.95   $136.00  
  Purchase #2 $31.86   4.585%   $33.3208   $33.32   $33.30   $33.30  
  Purchase #3 $179.82   4.134%   $187.2538   $187.25   $187.25   $187.30  
  Purchase #4 $86.93   3.869%   $90.2933   $90.29   $90.30   $90.30  
  Purchase #5 $222.50   10.695%   $246.2964   $246.30   $246.30   $246.30  
  Purchase #6 $18.52   7.164%   $19.8468   $19.85   $19.85   $19.80  
  Purchase #7 $229.51   5.553%   $242.2547   $242.25   $242.25   $242.30  
  7 purchase totals = $895.91       $955.2203   $955.21   $955.20   $955.30