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 $110.83   3.210%   $114.3876   $114.39   $114.40   $114.40  
  Purchase #2 $20.82   3.171%   $21.4802   $21.48   $21.50   $21.50  
  Purchase #3 $247.42   8.268%   $267.8767   $267.88   $267.90   $267.90  
  Purchase #4 $48.99   10.857%   $54.3088   $54.31   $54.30   $54.30  
  Purchase #5 $96.72   10.261%   $106.6444   $106.64   $106.65   $106.60  
  Purchase #6 $153.82   13.839%   $175.1071   $175.11   $175.10   $175.10  
  Purchase #7 $243.68   7.437%   $261.8025   $261.80   $261.80   $261.80  
  7 purchase totals = $922.28       $1,001.6073   $1,001.61   $1,001.65   $1,001.60