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 $61.26   6.113%   $65.0048   $65.00   $65.00   $65.00  
  Purchase #2 $28.35   4.633%   $29.6635   $29.66   $29.65   $29.70  
  Purchase #3 $138.84   5.309%   $146.211   $146.21   $146.20   $146.20  
  Purchase #4 $104.95   9.187%   $114.5918   $114.59   $114.60   $114.60  
  Purchase #5 $108.30   6.865%   $115.7348   $115.73   $115.75   $115.70  
  Purchase #6 $16.65   5.839%   $17.6222   $17.62   $17.60   $17.60  
  Purchase #7 $230.76   4.641%   $241.4696   $241.47   $241.45   $241.50  
  7 purchase totals = $689.11       $730.2977   $730.28   $730.25   $730.30