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 $156.93   13.327%   $177.8441   $177.84   $177.85   $177.80  
  Purchase #2 $39.65   10.585%   $43.847   $43.85   $43.85   $43.80  
  Purchase #3 $129.37   11.308%   $143.9992   $144.00   $144.00   $144.00  
  Purchase #4 $53.82   6.267%   $57.1929   $57.19   $57.20   $57.20  
  Purchase #5 $206.66   12.578%   $232.6537   $232.65   $232.65   $232.70  
  Purchase #6 $224.75   12.690%   $253.2708   $253.27   $253.25   $253.30  
  Purchase #7 $115.28   3.348%   $119.1396   $119.14   $119.15   $119.10  
  7 purchase totals = $926.46       $1,027.9473   $1,027.94   $1,027.95   $1,027.90