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 $165.48   12.201%   $185.6702   $185.67   $185.65   $185.70  
  Purchase #2 $161.97   13.812%   $184.3413   $184.34   $184.35   $184.30  
  Purchase #3 $117.36   13.615%   $133.3386   $133.34   $133.35   $133.30  
  Purchase #4 $226.28   7.832%   $244.0022   $244.00   $244.00   $244.00  
  Purchase #5 $143.33   10.117%   $157.8307   $157.83   $157.85   $157.80  
  Purchase #6 $14.92   11.842%   $16.6868   $16.69   $16.70   $16.70  
  Purchase #7 $70.84   5.484%   $74.7249   $74.72   $74.70   $74.70  
  7 purchase totals = $900.18       $996.5947   $996.59   $996.60   $996.50