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 $65.72   11.162%   $73.0557   $73.06   $73.05   $73.10  
  Purchase #2 $148.76   5.852%   $157.4654   $157.47   $157.45   $157.50  
  Purchase #3 $111.65   8.587%   $121.2374   $121.24   $121.25   $121.20  
  Purchase #4 $226.30   12.464%   $254.506   $254.51   $254.50   $254.50  
  Purchase #5 $203.76   3.195%   $210.2701   $210.27   $210.25   $210.30  
  Purchase #6 $92.83   7.335%   $99.6391   $99.64   $99.65   $99.60  
  Purchase #7 $92.39   11.494%   $103.0093   $103.01   $103.00   $103.00  
  7 purchase totals = $941.41       $1,019.1830   $1,019.20   $1,019.15   $1,019.20