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 $114.43   6.258%   $121.591   $121.59   $121.60   $121.60  
  Purchase #2 $107.64   6.124%   $114.2319   $114.23   $114.25   $114.20  
  Purchase #3 $60.69   5.531%   $64.0468   $64.05   $64.05   $64.00  
  Purchase #4 $106.61   5.748%   $112.7379   $112.74   $112.75   $112.70  
  Purchase #5 $238.50   11.506%   $265.9418   $265.94   $265.95   $265.90  
  Purchase #6 $249.82   3.485%   $258.5262   $258.53   $258.55   $258.50  
  Purchase #7 $172.52   4.215%   $179.7917   $179.79   $179.80   $179.80  
  7 purchase totals = $1,050.21       $1,116.8673   $1,116.87   $1,116.95   $1,116.70