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 $149.58   9.673%   $164.0489   $164.05   $164.05   $164.00  
  Purchase #2 $100.71   11.148%   $111.9372   $111.94   $111.95   $111.90  
  Purchase #3 $158.54   4.522%   $165.7092   $165.71   $165.70   $165.70  
  Purchase #4 $184.77   11.249%   $205.5548   $205.55   $205.55   $205.60  
  Purchase #5 $69.95   6.608%   $74.5723   $74.57   $74.55   $74.60  
  Purchase #6 $156.53   6.643%   $166.9283   $166.93   $166.95   $166.90  
  Purchase #7 $204.46   13.260%   $231.5714   $231.57   $231.55   $231.60  
  7 purchase totals = $1,024.54       $1,120.3221   $1,120.32   $1,120.30   $1,120.30