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 $42.54   4.797%   $44.5806   $44.58   $44.60   $44.60  
  Purchase #2 $41.47   12.760%   $46.7616   $46.76   $46.75   $46.80  
  Purchase #3 $114.89   7.353%   $123.3379   $123.34   $123.35   $123.30  
  Purchase #4 $235.92   11.436%   $262.8998   $262.90   $262.90   $262.90  
  Purchase #5 $187.59   5.165%   $197.279   $197.28   $197.30   $197.30  
  Purchase #6 $175.84   9.149%   $191.9276   $191.93   $191.95   $191.90  
  Purchase #7 $89.93   5.404%   $94.7898   $94.79   $94.80   $94.80  
  7 purchase totals = $888.18       $961.5763   $961.58   $961.65   $961.60