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 $208.96   9.743%   $229.319   $229.32   $229.30   $229.30  
  Purchase #2 $72.94   3.384%   $75.4083   $75.41   $75.40   $75.40  
  Purchase #3 $109.46   13.270%   $123.9853   $123.99   $124.00   $124.00  
  Purchase #4 $152.69   9.734%   $167.5528   $167.55   $167.55   $167.60  
  Purchase #5 $53.79   5.179%   $56.5758   $56.58   $56.60   $56.60  
  Purchase #6 $207.40   4.402%   $216.5297   $216.53   $216.55   $216.50  
  Purchase #7 $219.87   13.445%   $249.4315   $249.43   $249.45   $249.40  
  7 purchase totals = $1,025.11       $1,118.8024   $1,118.81   $1,118.85   $1,118.80