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 $246.37   6.762%   $263.0295   $263.03   $263.05   $263.00  
  Purchase #2 $158.44   7.470%   $170.2755   $170.28   $170.30   $170.30  
  Purchase #3 $43.43   4.102%   $45.2115   $45.21   $45.20   $45.20  
  Purchase #4 $155.65   6.292%   $165.4435   $165.44   $165.45   $165.40  
  Purchase #5 $197.91   10.182%   $218.0612   $218.06   $218.05   $218.10  
  Purchase #6 $126.90   9.623%   $139.1116   $139.11   $139.10   $139.10  
  Purchase #7 $16.33   6.315%   $17.3612   $17.36   $17.35   $17.40  
  7 purchase totals = $945.03       $1,018.4940   $1,018.49   $1,018.50   $1,018.50