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 $52.84   11.630%   $58.9853   $58.99   $59.00   $59.00  
  Purchase #2 $223.36   5.618%   $235.9084   $235.91   $235.90   $235.90  
  Purchase #3 $167.27   6.251%   $177.726   $177.73   $177.75   $177.70  
  Purchase #4 $61.82   13.222%   $69.9938   $69.99   $70.00   $70.00  
  Purchase #5 $101.55   6.114%   $107.7588   $107.76   $107.75   $107.80  
  Purchase #6 $14.31   4.220%   $14.9139   $14.91   $14.90   $14.90  
  Purchase #7 $103.73   8.783%   $112.8406   $112.84   $112.85   $112.80  
  7 purchase totals = $724.88       $778.1268   $778.13   $778.15   $778.10