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 $232.94   5.852%   $246.5716   $246.57   $246.55   $246.60  
  Purchase #2 $131.45   8.179%   $142.2013   $142.20   $142.20   $142.20  
  Purchase #3 $35.64   3.582%   $36.9166   $36.92   $36.90   $36.90  
  Purchase #4 $124.32   6.191%   $132.0167   $132.02   $132.00   $132.00  
  Purchase #5 $164.68   6.693%   $175.702   $175.70   $175.70   $175.70  
  Purchase #6 $200.56   9.378%   $219.3685   $219.37   $219.35   $219.40  
  Purchase #7 $177.99   9.206%   $194.3758   $194.38   $194.40   $194.40  
  7 purchase totals = $1,067.58       $1,147.1525   $1,147.16   $1,147.10   $1,147.20