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 $85.80   9.517%   $93.9656   $93.97   $93.95   $94.00  
  Purchase #2 $147.56   4.665%   $154.4437   $154.44   $154.45   $154.40  
  Purchase #3 $81.32   8.260%   $88.037   $88.04   $88.05   $88.00  
  Purchase #4 $218.75   3.599%   $226.6228   $226.62   $226.60   $226.60  
  Purchase #5 $177.88   12.862%   $200.7589   $200.76   $200.75   $200.80  
  Purchase #6 $165.93   12.702%   $187.0064   $187.01   $187.00   $187.00  
  Purchase #7 $50.33   12.170%   $56.4552   $56.46   $56.45   $56.50  
  7 purchase totals = $927.57       $1,007.2896   $1,007.30   $1,007.25   $1,007.30