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 $56.70   7.586%   $61.0013   $61.00   $61.00   $61.00  
  Purchase #2 $143.77   7.568%   $154.6505   $154.65   $154.65   $154.70  
  Purchase #3 $88.90   5.321%   $93.6304   $93.63   $93.65   $93.60  
  Purchase #4 $218.47   5.511%   $230.5099   $230.51   $230.50   $230.50  
  Purchase #5 $182.69   4.469%   $190.8544   $190.85   $190.85   $190.90  
  Purchase #6 $150.41   3.187%   $155.2036   $155.20   $155.20   $155.20  
  Purchase #7 $165.28   5.699%   $174.6993   $174.70   $174.70   $174.70  
  7 purchase totals = $1,006.22       $1,060.5494   $1,060.54   $1,060.55   $1,060.60