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 $103.38   9.310%   $113.0047   $113.00   $113.00   $113.00  
  Purchase #2 $87.60   10.350%   $96.6666   $96.67   $96.65   $96.70  
  Purchase #3 $24.87   8.203%   $26.9101   $26.91   $26.90   $26.90  
  Purchase #4 $160.33   11.798%   $179.2457   $179.25   $179.25   $179.20  
  Purchase #5 $66.52   13.854%   $75.7357   $75.74   $75.75   $75.70  
  Purchase #6 $247.69   13.260%   $280.5337   $280.53   $280.55   $280.50  
  Purchase #7 $217.68   12.556%   $245.0119   $245.01   $245.00   $245.00  
  7 purchase totals = $908.07       $1,017.1084   $1,017.11   $1,017.10   $1,017.00