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 $178.55   10.572%   $197.4263   $197.43   $197.45   $197.40  
  Purchase #2 $156.41   12.431%   $175.8533   $175.85   $175.85   $175.90  
  Purchase #3 $127.52   5.110%   $134.0363   $134.04   $134.05   $134.00  
  Purchase #4 $22.92   13.835%   $26.091   $26.09   $26.10   $26.10  
  Purchase #5 $242.86   8.869%   $264.3993   $264.40   $264.40   $264.40  
  Purchase #6 $158.69   8.762%   $172.5944   $172.59   $172.60   $172.60  
  Purchase #7 $177.83   9.120%   $194.0481   $194.05   $194.05   $194.00  
  7 purchase totals = $1,064.78       $1,164.4487   $1,164.45   $1,164.50   $1,164.40