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 $161.98   12.457%   $182.1578   $182.16   $182.15   $182.20  
  Purchase #2 $245.31   11.846%   $274.3694   $274.37   $274.35   $274.40  
  Purchase #3 $65.58   13.744%   $74.5933   $74.59   $74.60   $74.60  
  Purchase #4 $66.70   6.753%   $71.2043   $71.20   $71.20   $71.20  
  Purchase #5 $226.46   6.789%   $241.8344   $241.83   $241.85   $241.80  
  Purchase #6 $216.87   11.653%   $242.1419   $242.14   $242.15   $242.10  
  Purchase #7 $14.88   9.860%   $16.3472   $16.35   $16.35   $16.30  
  7 purchase totals = $997.78       $1,102.6483   $1,102.64   $1,102.65   $1,102.60