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 $41.97   6.368%   $44.6426   $44.64   $44.65   $44.60  
  Purchase #2 $58.68   3.432%   $60.6939   $60.69   $60.70   $60.70  
  Purchase #3 $183.51   13.318%   $207.9499   $207.95   $207.95   $207.90  
  Purchase #4 $185.99   5.556%   $196.3236   $196.32   $196.30   $196.30  
  Purchase #5 $200.62   5.565%   $211.7845   $211.78   $211.80   $211.80  
  Purchase #6 $160.58   9.184%   $175.3277   $175.33   $175.35   $175.30  
  Purchase #7 $129.84   12.855%   $146.5309   $146.53   $146.55   $146.50  
  7 purchase totals = $961.19       $1,043.2531   $1,043.24   $1,043.30   $1,043.10