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 $168.37   10.641%   $186.2863   $186.29   $186.30   $186.30  
  Purchase #2 $102.43   8.278%   $110.9092   $110.91   $110.90   $110.90  
  Purchase #3 $59.97   12.222%   $67.2995   $67.30   $67.30   $67.30  
  Purchase #4 $187.60   8.873%   $204.2457   $204.25   $204.25   $204.20  
  Purchase #5 $168.75   6.112%   $179.064   $179.06   $179.05   $179.10  
  Purchase #6 $203.32   9.389%   $222.4097   $222.41   $222.40   $222.40  
  Purchase #7 $163.63   12.390%   $183.9038   $183.90   $183.90   $183.90  
  7 purchase totals = $1,054.07       $1,154.1182   $1,154.12   $1,154.10   $1,154.10