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 $59.66   5.752%   $63.0916   $63.09   $63.10   $63.10  
  Purchase #2 $126.33   4.103%   $131.5133   $131.51   $131.50   $131.50  
  Purchase #3 $179.27   6.524%   $190.9656   $190.97   $190.95   $191.00  
  Purchase #4 $87.95   9.655%   $96.4416   $96.44   $96.45   $96.40  
  Purchase #5 $77.25   8.572%   $83.8719   $83.87   $83.85   $83.90  
  Purchase #6 $234.32   5.343%   $246.8397   $246.84   $246.85   $246.80  
  Purchase #7 $60.51   9.369%   $66.1792   $66.18   $66.20   $66.20  
  7 purchase totals = $825.29       $878.9029   $878.90   $878.90   $878.90