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 $151.45   13.206%   $171.4505   $171.45   $171.45   $171.50  
  Purchase #2 $233.53   6.563%   $248.8566   $248.86   $248.85   $248.90  
  Purchase #3 $38.82   5.566%   $40.9807   $40.98   $41.00   $41.00  
  Purchase #4 $231.97   5.759%   $245.3292   $245.33   $245.35   $245.30  
  Purchase #5 $155.90   12.439%   $175.2924   $175.29   $175.30   $175.30  
  Purchase #6 $224.81   12.380%   $252.6415   $252.64   $252.65   $252.60  
  Purchase #7 $22.94   12.690%   $25.8511   $25.85   $25.85   $25.90  
  7 purchase totals = $1,059.42       $1,160.4020   $1,160.40   $1,160.45   $1,160.50