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 $79.42   8.546%   $86.2072   $86.21   $86.20   $86.20  
  Purchase #2 $231.78   4.381%   $241.9343   $241.93   $241.95   $241.90  
  Purchase #3 $159.78   11.261%   $177.7728   $177.77   $177.75   $177.80  
  Purchase #4 $123.56   12.491%   $138.9939   $138.99   $139.00   $139.00  
  Purchase #5 $191.26   9.396%   $209.2308   $209.23   $209.25   $209.20  
  Purchase #6 $45.53   13.472%   $51.6638   $51.66   $51.65   $51.70  
  Purchase #7 $114.89   4.861%   $120.4748   $120.47   $120.45   $120.50  
  7 purchase totals = $946.22       $1,026.2776   $1,026.26   $1,026.25   $1,026.30