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 $152.70   10.212%   $168.2937   $168.29   $168.30   $168.30  
  Purchase #2 $90.79   13.216%   $102.7888   $102.79   $102.80   $102.80  
  Purchase #3 $226.79   12.671%   $255.5266   $255.53   $255.55   $255.50  
  Purchase #4 $83.71   10.542%   $92.5347   $92.53   $92.55   $92.50  
  Purchase #5 $176.39   12.349%   $198.1724   $198.17   $198.15   $198.20  
  Purchase #6 $187.90   6.627%   $200.3521   $200.35   $200.35   $200.40  
  Purchase #7 $189.32   9.157%   $206.656   $206.66   $206.65   $206.70  
  7 purchase totals = $1,107.60       $1,224.3243   $1,224.32   $1,224.35   $1,224.40