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 $150.79   10.756%   $167.009   $167.01   $167.00   $167.00  
  Purchase #2 $126.81   9.335%   $138.6477   $138.65   $138.65   $138.60  
  Purchase #3 $125.66   12.132%   $140.9051   $140.91   $140.90   $140.90  
  Purchase #4 $248.49   12.162%   $278.7114   $278.71   $278.70   $278.70  
  Purchase #5 $187.41   9.799%   $205.7743   $205.77   $205.75   $205.80  
  Purchase #6 $133.93   7.454%   $143.9131   $143.91   $143.90   $143.90  
  Purchase #7 $56.46   4.602%   $59.0583   $59.06   $59.05   $59.10  
  7 purchase totals = $1,029.55       $1,134.0189   $1,134.02   $1,133.95   $1,134.00