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 $203.85   11.279%   $226.8422   $226.84   $226.85   $226.80  
  Purchase #2 $30.25   13.569%   $34.3546   $34.35   $34.35   $34.40  
  Purchase #3 $240.39   3.819%   $249.5705   $249.57   $249.55   $249.60  
  Purchase #4 $247.37   7.488%   $265.8931   $265.89   $265.90   $265.90  
  Purchase #5 $160.69   6.211%   $170.6705   $170.67   $170.65   $170.70  
  Purchase #6 $42.97   9.705%   $47.1402   $47.14   $47.15   $47.10  
  Purchase #7 $248.34   7.510%   $266.9903   $266.99   $267.00   $267.00  
  7 purchase totals = $1,173.86       $1,261.4614   $1,261.45   $1,261.45   $1,261.50