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 $186.66   9.461%   $204.3199   $204.32   $204.30   $204.30  
  Purchase #2 $82.37   5.439%   $86.8501   $86.85   $86.85   $86.90  
  Purchase #3 $115.34   13.114%   $130.4657   $130.47   $130.45   $130.50  
  Purchase #4 $147.81   10.126%   $162.7772   $162.78   $162.80   $162.80  
  Purchase #5 $183.91   10.254%   $202.7681   $202.77   $202.75   $202.80  
  Purchase #6 $175.50   6.401%   $186.7338   $186.73   $186.75   $186.70  
  Purchase #7 $75.52   12.173%   $84.713   $84.71   $84.70   $84.70  
  7 purchase totals = $967.11       $1,058.6278   $1,058.63   $1,058.60   $1,058.70