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 $76.55   4.102%   $79.6901   $79.69   $79.70   $79.70  
  Purchase #2 $183.64   11.656%   $205.0451   $205.05   $205.05   $205.00  
  Purchase #3 $155.43   13.326%   $176.1426   $176.14   $176.15   $176.10  
  Purchase #4 $102.97   12.673%   $116.0194   $116.02   $116.00   $116.00  
  Purchase #5 $118.82   13.743%   $135.1494   $135.15   $135.15   $135.10  
  Purchase #6 $231.91   9.226%   $253.306   $253.31   $253.30   $253.30  
  Purchase #7 $153.58   11.758%   $171.6379   $171.64   $171.65   $171.60  
  7 purchase totals = $1,022.90       $1,136.9905   $1,137.00   $1,137.00   $1,136.80