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 $136.76   10.782%   $151.5055   $151.51   $151.50   $151.50  
  Purchase #2 $198.91   7.209%   $213.2494   $213.25   $213.25   $213.20  
  Purchase #3 $31.48   9.363%   $34.4275   $34.43   $34.45   $34.40  
  Purchase #4 $227.35   6.161%   $241.357   $241.36   $241.35   $241.40  
  Purchase #5 $67.37   3.298%   $69.5919   $69.59   $69.60   $69.60  
  Purchase #6 $24.25   3.816%   $25.1754   $25.18   $25.20   $25.20  
  Purchase #7 $102.80   3.310%   $106.2027   $106.20   $106.20   $106.20  
  7 purchase totals = $788.92       $841.5094   $841.52   $841.55   $841.50