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 $219.26   10.137%   $241.4864   $241.49   $241.50   $241.50  
  Purchase #2 $110.39   7.482%   $118.6494   $118.65   $118.65   $118.60  
  Purchase #3 $27.95   4.638%   $29.2463   $29.25   $29.25   $29.20  
  Purchase #4 $209.48   3.547%   $216.9103   $216.91   $216.90   $216.90  
  Purchase #5 $48.44   3.597%   $50.1824   $50.18   $50.20   $50.20  
  Purchase #6 $125.69   4.828%   $131.7583   $131.76   $131.75   $131.80  
  Purchase #7 $125.25   11.751%   $139.9681   $139.97   $139.95   $140.00  
  7 purchase totals = $866.46       $928.2012   $928.21   $928.20   $928.20