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 $14.83   12.317%   $16.6566   $16.66   $16.65   $16.70  
  Purchase #2 $238.66   8.538%   $259.0368   $259.04   $259.05   $259.00  
  Purchase #3 $99.82   11.470%   $111.2694   $111.27   $111.25   $111.30  
  Purchase #4 $58.91   9.611%   $64.5718   $64.57   $64.55   $64.60  
  Purchase #5 $207.47   6.372%   $220.69   $220.69   $220.70   $220.70  
  Purchase #6 $116.59   9.796%   $128.0112   $128.01   $128.00   $128.00  
  Purchase #7 $188.89   13.824%   $215.0022   $215.00   $215.00   $215.00  
  7 purchase totals = $925.17       $1,015.2380   $1,015.24   $1,015.20   $1,015.30