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 $187.61   5.822%   $198.5327   $198.53   $198.55   $198.50  
  Purchase #2 $81.57   7.716%   $87.8639   $87.86   $87.85   $87.90  
  Purchase #3 $206.30   5.758%   $218.1788   $218.18   $218.20   $218.20  
  Purchase #4 $88.49   9.349%   $96.7629   $96.76   $96.75   $96.80  
  Purchase #5 $56.86   4.706%   $59.5358   $59.54   $59.55   $59.50  
  Purchase #6 $49.31   10.248%   $54.3633   $54.36   $54.35   $54.40  
  Purchase #7 $122.49   8.320%   $132.6812   $132.68   $132.70   $132.70  
  7 purchase totals = $792.63       $847.9186   $847.91   $847.95   $848.00