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 $113.68   8.790%   $123.6725   $123.67   $123.65   $123.70  
  Purchase #2 $124.62   3.686%   $129.2135   $129.21   $129.20   $129.20  
  Purchase #3 $147.77   4.577%   $154.5334   $154.53   $154.55   $154.50  
  Purchase #4 $201.93   8.575%   $219.2455   $219.25   $219.25   $219.20  
  Purchase #5 $153.93   11.780%   $172.063   $172.06   $172.05   $172.10  
  Purchase #6 $93.81   5.590%   $99.054   $99.05   $99.05   $99.10  
  Purchase #7 $127.51   6.543%   $135.853   $135.85   $135.85   $135.90  
  7 purchase totals = $963.25       $1,033.6349   $1,033.62   $1,033.60   $1,033.70