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 $185.72   10.367%   $204.9736   $204.97   $204.95   $205.00  
  Purchase #2 $57.53   6.640%   $61.35   $61.35   $61.35   $61.40  
  Purchase #3 $161.29   4.147%   $167.9787   $167.98   $168.00   $168.00  
  Purchase #4 $130.62   11.375%   $145.478   $145.48   $145.50   $145.50  
  Purchase #5 $116.25   3.388%   $120.1886   $120.19   $120.20   $120.20  
  Purchase #6 $59.25   7.358%   $63.6096   $63.61   $63.60   $63.60  
  Purchase #7 $130.44   4.847%   $136.7624   $136.76   $136.75   $136.80  
  7 purchase totals = $841.10       $900.3409   $900.34   $900.35   $900.50