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 $82.52   11.794%   $92.2524   $92.25   $92.25   $92.30  
  Purchase #2 $148.98   8.178%   $161.1636   $161.16   $161.15   $161.20  
  Purchase #3 $225.61   8.161%   $244.022   $244.02   $244.00   $244.00  
  Purchase #4 $6.69   12.556%   $7.53   $7.53   $7.55   $7.50  
  Purchase #5 $233.39   6.261%   $248.0025   $248.00   $248.00   $248.00  
  Purchase #6 $105.52   3.437%   $109.1467   $109.15   $109.15   $109.10  
  Purchase #7 $26.82   3.820%   $27.8445   $27.84   $27.85   $27.80  
  7 purchase totals = $829.53       $889.9617   $889.95   $889.95   $889.90