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 $119.37   12.115%   $133.8317   $133.83   $133.85   $133.80  
  Purchase #2 $228.38   12.386%   $256.6671   $256.67   $256.65   $256.70  
  Purchase #3 $33.65   8.874%   $36.6361   $36.64   $36.65   $36.60  
  Purchase #4 $84.32   10.661%   $93.3094   $93.31   $93.30   $93.30  
  Purchase #5 $206.82   4.648%   $216.433   $216.43   $216.45   $216.40  
  Purchase #6 $50.51   13.280%   $57.2177   $57.22   $57.20   $57.20  
  Purchase #7 $201.25   7.542%   $216.4283   $216.43   $216.45   $216.40  
  7 purchase totals = $924.30       $1,010.5233   $1,010.53   $1,010.55   $1,010.40