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 $246.73   5.250%   $259.6833   $259.68   $259.70   $259.70  
  Purchase #2 $8.52   4.772%   $8.9266   $8.93   $8.95   $8.90  
  Purchase #3 $74.74   3.832%   $77.604   $77.60   $77.60   $77.60  
  Purchase #4 $103.90   11.451%   $115.7976   $115.80   $115.80   $115.80  
  Purchase #5 $201.37   4.217%   $209.8618   $209.86   $209.85   $209.90  
  Purchase #6 $126.89   13.379%   $143.8666   $143.87   $143.85   $143.90  
  Purchase #7 $75.65   4.175%   $78.8084   $78.81   $78.80   $78.80  
  7 purchase totals = $837.80       $894.5483   $894.55   $894.55   $894.60