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 $64.49   5.204%   $67.8461   $67.85   $67.85   $67.80  
  Purchase #2 $203.32   6.193%   $215.9116   $215.91   $215.90   $215.90  
  Purchase #3 $22.96   5.845%   $24.302   $24.30   $24.30   $24.30  
  Purchase #4 $197.93   12.318%   $222.311   $222.31   $222.30   $222.30  
  Purchase #5 $205.78   12.717%   $231.949   $231.95   $231.95   $231.90  
  Purchase #6 $162.88   12.847%   $183.8052   $183.81   $183.80   $183.80  
  Purchase #7 $108.65   12.799%   $122.5561   $122.56   $122.55   $122.60  
  7 purchase totals = $966.01       $1,068.6810   $1,068.69   $1,068.65   $1,068.60