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 $212.85   11.629%   $237.6023   $237.60   $237.60   $237.60  
  Purchase #2 $67.46   10.393%   $74.4711   $74.47   $74.45   $74.50  
  Purchase #3 $197.87   3.395%   $204.5877   $204.59   $204.60   $204.60  
  Purchase #4 $60.26   3.405%   $62.3119   $62.31   $62.30   $62.30  
  Purchase #5 $207.81   9.699%   $227.9655   $227.97   $227.95   $228.00  
  Purchase #6 $116.72   12.321%   $131.1011   $131.10   $131.10   $131.10  
  Purchase #7 $219.43   13.627%   $249.3317   $249.33   $249.35   $249.30  
  7 purchase totals = $1,082.40       $1,187.3713   $1,187.37   $1,187.35   $1,187.40