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 $35.99   4.429%   $37.584   $37.58   $37.60   $37.60  
  Purchase #2 $24.91   3.584%   $25.8028   $25.80   $25.80   $25.80  
  Purchase #3 $37.53   7.302%   $40.2704   $40.27   $40.25   $40.30  
  Purchase #4 $193.47   9.342%   $211.544   $211.54   $211.55   $211.50  
  Purchase #5 $219.55   3.169%   $226.5075   $226.51   $226.50   $226.50  
  Purchase #6 $193.91   13.172%   $219.4518   $219.45   $219.45   $219.50  
  Purchase #7 $245.38   10.586%   $271.3559   $271.36   $271.35   $271.40  
  7 purchase totals = $950.74       $1,032.5164   $1,032.51   $1,032.50   $1,032.60