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 $234.90   13.701%   $267.0836   $267.08   $267.10   $267.10  
  Purchase #2 $66.81   12.856%   $75.3991   $75.40   $75.40   $75.40  
  Purchase #3 $209.49   6.535%   $223.1802   $223.18   $223.20   $223.20  
  Purchase #4 $117.73   4.201%   $122.6758   $122.68   $122.70   $122.70  
  Purchase #5 $93.88   3.217%   $96.9001   $96.90   $96.90   $96.90  
  Purchase #6 $104.96   12.411%   $117.9866   $117.99   $118.00   $118.00  
  Purchase #7 $40.58   10.284%   $44.7532   $44.75   $44.75   $44.80  
  7 purchase totals = $868.35       $947.9786   $947.98   $948.05   $948.10