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 $176.65   5.627%   $186.5901   $186.59   $186.60   $186.60  
  Purchase #2 $223.74   11.317%   $249.0607   $249.06   $249.05   $249.10  
  Purchase #3 $56.71   7.811%   $61.1396   $61.14   $61.15   $61.10  
  Purchase #4 $109.61   8.868%   $119.3302   $119.33   $119.35   $119.30  
  Purchase #5 $109.59   11.362%   $122.0416   $122.04   $122.05   $122.00  
  Purchase #6 $102.44   4.816%   $107.3735   $107.37   $107.35   $107.40  
  Purchase #7 $38.37   5.725%   $40.5667   $40.57   $40.55   $40.60  
  7 purchase totals = $817.11       $886.1024   $886.10   $886.10   $886.10