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 $185.95   8.480%   $201.7186   $201.72   $201.70   $201.70  
  Purchase #2 $86.65   9.555%   $94.9294   $94.93   $94.95   $94.90  
  Purchase #3 $82.27   13.671%   $93.5171   $93.52   $93.50   $93.50  
  Purchase #4 $238.41   13.819%   $271.3559   $271.36   $271.35   $271.40  
  Purchase #5 $231.74   11.135%   $257.5442   $257.54   $257.55   $257.50  
  Purchase #6 $247.76   7.126%   $265.4154   $265.42   $265.40   $265.40  
  Purchase #7 $40.27   6.446%   $42.8658   $42.87   $42.85   $42.90  
  7 purchase totals = $1,113.05       $1,227.3464   $1,227.36   $1,227.30   $1,227.30