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 $174.30   13.601%   $198.0065   $198.01   $198.00   $198.00  
  Purchase #2 $202.74   12.341%   $227.7601   $227.76   $227.75   $227.80  
  Purchase #3 $147.76   4.418%   $154.288   $154.29   $154.30   $154.30  
  Purchase #4 $73.81   3.354%   $76.2856   $76.29   $76.30   $76.30  
  Purchase #5 $54.36   3.198%   $56.0984   $56.10   $56.10   $56.10  
  Purchase #6 $80.88   8.259%   $87.5599   $87.56   $87.55   $87.60  
  Purchase #7 $181.73   12.751%   $204.9024   $204.90   $204.90   $204.90  
  7 purchase totals = $915.58       $1,004.9009   $1,004.91   $1,004.90   $1,005.00