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 $202.83   8.759%   $220.5959   $220.60   $220.60   $220.60  
  Purchase #2 $72.67   4.588%   $76.0041   $76.00   $76.00   $76.00  
  Purchase #3 $60.85   10.322%   $67.1309   $67.13   $67.15   $67.10  
  Purchase #4 $173.92   13.263%   $196.987   $196.99   $197.00   $197.00  
  Purchase #5 $166.93   6.391%   $177.5985   $177.60   $177.60   $177.60  
  Purchase #6 $49.30   9.717%   $54.0905   $54.09   $54.10   $54.10  
  Purchase #7 $229.70   9.520%   $251.5674   $251.57   $251.55   $251.60  
  7 purchase totals = $956.20       $1,043.9743   $1,043.98   $1,044.00   $1,044.00