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 $164.58   13.851%   $187.376   $187.38   $187.40   $187.40  
  Purchase #2 $211.87   11.830%   $236.9342   $236.93   $236.95   $236.90  
  Purchase #3 $152.65   13.769%   $173.6684   $173.67   $173.65   $173.70  
  Purchase #4 $37.99   9.413%   $41.566   $41.57   $41.55   $41.60  
  Purchase #5 $7.46   9.115%   $8.14   $8.14   $8.15   $8.10  
  Purchase #6 $161.83   8.641%   $175.8137   $175.81   $175.80   $175.80  
  Purchase #7 $184.34   5.489%   $194.4584   $194.46   $194.45   $194.50  
  7 purchase totals = $920.72       $1,017.9567   $1,017.96   $1,017.95   $1,018.00