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 $65.29   12.481%   $73.4388   $73.44   $73.45   $73.40  
  Purchase #2 $49.87   4.673%   $52.2004   $52.20   $52.20   $52.20  
  Purchase #3 $111.69   13.416%   $126.6743   $126.67   $126.65   $126.70  
  Purchase #4 $232.33   4.264%   $242.2366   $242.24   $242.25   $242.20  
  Purchase #5 $115.59   5.473%   $121.9162   $121.92   $121.90   $121.90  
  Purchase #6 $172.83   10.383%   $190.7749   $190.77   $190.75   $190.80  
  Purchase #7 $248.39   10.837%   $275.308   $275.31   $275.30   $275.30  
  7 purchase totals = $995.99       $1,082.5492   $1,082.55   $1,082.50   $1,082.50