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 $48.31   4.209%   $50.3434   $50.34   $50.35   $50.30  
  Purchase #2 $232.92   6.156%   $247.2586   $247.26   $247.25   $247.30  
  Purchase #3 $167.56   10.819%   $185.6883   $185.69   $185.70   $185.70  
  Purchase #4 $212.84   8.262%   $230.4248   $230.42   $230.40   $230.40  
  Purchase #5 $47.50   10.122%   $52.308   $52.31   $52.30   $52.30  
  Purchase #6 $38.53   13.771%   $43.836   $43.84   $43.85   $43.80  
  Purchase #7 $39.93   3.783%   $41.4406   $41.44   $41.45   $41.40  
  7 purchase totals = $787.59       $851.2997   $851.30   $851.30   $851.20