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 $56.83   11.369%   $63.291   $63.29   $63.30   $63.30  
  Purchase #2 $63.89   4.786%   $66.9478   $66.95   $66.95   $66.90  
  Purchase #3 $96.97   13.561%   $110.1201   $110.12   $110.10   $110.10  
  Purchase #4 $75.92   7.360%   $81.5077   $81.51   $81.50   $81.50  
  Purchase #5 $168.32   3.621%   $174.4149   $174.41   $174.40   $174.40  
  Purchase #6 $219.46   10.544%   $242.5999   $242.60   $242.60   $242.60  
  Purchase #7 $96.67   10.232%   $106.5613   $106.56   $106.55   $106.60  
  7 purchase totals = $778.06       $845.4427   $845.44   $845.40   $845.40