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 $49.38   6.802%   $52.7388   $52.74   $52.75   $52.70  
  Purchase #2 $205.81   10.218%   $226.8397   $226.84   $226.85   $226.80  
  Purchase #3 $242.52   6.116%   $257.3525   $257.35   $257.35   $257.40  
  Purchase #4 $234.74   5.154%   $246.8385   $246.84   $246.85   $246.80  
  Purchase #5 $10.30   5.169%   $10.8324   $10.83   $10.85   $10.80  
  Purchase #6 $248.85   8.180%   $269.2059   $269.21   $269.20   $269.20  
  Purchase #7 $235.97   13.467%   $267.7481   $267.75   $267.75   $267.70  
  7 purchase totals = $1,227.57       $1,331.5559   $1,331.56   $1,331.60   $1,331.40