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 $187.62   9.236%   $204.9486   $204.95   $204.95   $204.90  
  Purchase #2 $231.74   8.438%   $251.2942   $251.29   $251.30   $251.30  
  Purchase #3 $159.97   4.439%   $167.0711   $167.07   $167.05   $167.10  
  Purchase #4 $21.58   7.622%   $23.2248   $23.22   $23.20   $23.20  
  Purchase #5 $128.30   9.526%   $140.5219   $140.52   $140.50   $140.50  
  Purchase #6 $182.81   8.288%   $197.9613   $197.96   $197.95   $198.00  
  Purchase #7 $38.76   6.773%   $41.3852   $41.39   $41.40   $41.40  
  7 purchase totals = $950.78       $1,026.4071   $1,026.40   $1,026.35   $1,026.40