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 $78.41   10.624%   $86.7403   $86.74   $86.75   $86.70  
  Purchase #2 $53.68   4.852%   $56.2846   $56.28   $56.30   $56.30  
  Purchase #3 $180.29   12.363%   $202.5793   $202.58   $202.60   $202.60  
  Purchase #4 $205.32   9.207%   $224.2238   $224.22   $224.20   $224.20  
  Purchase #5 $84.50   4.259%   $88.0989   $88.10   $88.10   $88.10  
  Purchase #6 $238.48   8.593%   $258.9726   $258.97   $258.95   $259.00  
  Purchase #7 $195.41   7.549%   $210.1615   $210.16   $210.15   $210.20  
  7 purchase totals = $1,036.09       $1,127.0610   $1,127.05   $1,127.05   $1,127.10