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 $41.27   8.183%   $44.6471   $44.65   $44.65   $44.60  
  Purchase #2 $63.76   11.318%   $70.9764   $70.98   $71.00   $71.00  
  Purchase #3 $118.75   4.381%   $123.9524   $123.95   $123.95   $124.00  
  Purchase #4 $126.26   7.115%   $135.2434   $135.24   $135.25   $135.20  
  Purchase #5 $130.98   10.847%   $145.1874   $145.19   $145.20   $145.20  
  Purchase #6 $214.26   9.319%   $234.2269   $234.23   $234.25   $234.20  
  Purchase #7 $224.93   3.415%   $232.6114   $232.61   $232.60   $232.60  
  7 purchase totals = $920.21       $986.8450   $986.85   $986.90   $986.80