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 $233.94   5.267%   $246.2616   $246.26   $246.25   $246.30  
  Purchase #2 $134.97   5.596%   $142.5229   $142.52   $142.50   $142.50  
  Purchase #3 $54.90   5.142%   $57.723   $57.72   $57.70   $57.70  
  Purchase #4 $123.52   8.657%   $134.2131   $134.21   $134.20   $134.20  
  Purchase #5 $205.98   8.394%   $223.27   $223.27   $223.25   $223.30  
  Purchase #6 $244.81   8.643%   $265.9689   $265.97   $265.95   $266.00  
  Purchase #7 $128.79   5.420%   $135.7704   $135.77   $135.75   $135.80  
  7 purchase totals = $1,126.91       $1,205.7299   $1,205.72   $1,205.60   $1,205.80