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 $196.81   13.327%   $223.0389   $223.04   $223.05   $223.00  
  Purchase #2 $81.99   3.494%   $84.8547   $84.85   $84.85   $84.90  
  Purchase #3 $197.87   7.126%   $211.9702   $211.97   $211.95   $212.00  
  Purchase #4 $186.89   5.482%   $197.1353   $197.14   $197.15   $197.10  
  Purchase #5 $165.57   11.156%   $184.041   $184.04   $184.05   $184.00  
  Purchase #6 $10.44   13.690%   $11.8692   $11.87   $11.85   $11.90  
  Purchase #7 $154.48   4.293%   $161.1118   $161.11   $161.10   $161.10  
  7 purchase totals = $994.05       $1,074.0211   $1,074.02   $1,074.00   $1,074.00