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 $67.54   13.481%   $76.6451   $76.65   $76.65   $76.60  
  Purchase #2 $184.88   9.200%   $201.889   $201.89   $201.90   $201.90  
  Purchase #3 $49.73   13.358%   $56.3729   $56.37   $56.35   $56.40  
  Purchase #4 $26.52   5.791%   $28.0558   $28.06   $28.05   $28.10  
  Purchase #5 $35.87   4.236%   $37.3895   $37.39   $37.40   $37.40  
  Purchase #6 $7.73   4.454%   $8.0743   $8.07   $8.05   $8.10  
  Purchase #7 $64.29   3.856%   $66.769   $66.77   $66.75   $66.80  
  7 purchase totals = $436.56       $475.1956   $475.20   $475.15   $475.30