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 $85.79   13.704%   $97.5467   $97.55   $97.55   $97.50  
  Purchase #2 $140.52   10.862%   $155.7833   $155.78   $155.80   $155.80  
  Purchase #3 $16.79   13.170%   $19.0012   $19.00   $19.00   $19.00  
  Purchase #4 $227.89   13.813%   $259.3684   $259.37   $259.35   $259.40  
  Purchase #5 $72.94   13.403%   $82.7161   $82.72   $82.70   $82.70  
  Purchase #6 $190.26   8.143%   $205.7529   $205.75   $205.75   $205.80  
  Purchase #7 $228.62   4.766%   $239.516   $239.52   $239.50   $239.50  
  7 purchase totals = $962.81       $1,059.6846   $1,059.69   $1,059.65   $1,059.70