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 $184.58   3.654%   $191.3246   $191.32   $191.30   $191.30  
  Purchase #2 $79.65   8.428%   $86.3629   $86.36   $86.35   $86.40  
  Purchase #3 $229.32   9.608%   $251.3531   $251.35   $251.35   $251.40  
  Purchase #4 $248.45   5.467%   $262.0328   $262.03   $262.05   $262.00  
  Purchase #5 $245.78   3.413%   $254.1685   $254.17   $254.15   $254.20  
  Purchase #6 $116.96   4.198%   $121.87   $121.87   $121.85   $121.90  
  Purchase #7 $158.53   10.113%   $174.5621   $174.56   $174.55   $174.60  
  7 purchase totals = $1,263.27       $1,341.6740   $1,341.66   $1,341.60   $1,341.80