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 $201.26   12.248%   $225.9103   $225.91   $225.90   $225.90  
  Purchase #2 $211.75   12.664%   $238.566   $238.57   $238.55   $238.60  
  Purchase #3 $29.97   6.802%   $32.0086   $32.01   $32.00   $32.00  
  Purchase #4 $189.82   13.547%   $215.5349   $215.53   $215.55   $215.50  
  Purchase #5 $40.32   7.262%   $43.248   $43.25   $43.25   $43.20  
  Purchase #6 $239.87   7.251%   $257.263   $257.26   $257.25   $257.30  
  Purchase #7 $113.81   8.795%   $123.8196   $123.82   $123.80   $123.80  
  7 purchase totals = $1,026.80       $1,136.3504   $1,136.35   $1,136.30   $1,136.30