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 $88.94   5.462%   $93.7979   $93.80   $93.80   $93.80  
  Purchase #2 $218.99   9.192%   $239.1196   $239.12   $239.10   $239.10  
  Purchase #3 $113.59   12.270%   $127.5275   $127.53   $127.55   $127.50  
  Purchase #4 $23.98   12.619%   $27.006   $27.01   $27.00   $27.00  
  Purchase #5 $206.81   3.531%   $214.1125   $214.11   $214.10   $214.10  
  Purchase #6 $174.90   10.694%   $193.6038   $193.60   $193.60   $193.60  
  Purchase #7 $167.63   9.510%   $183.5716   $183.57   $183.55   $183.60  
  7 purchase totals = $994.84       $1,078.7389   $1,078.74   $1,078.70   $1,078.70