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 $46.46   8.624%   $50.4667   $50.47   $50.45   $50.50  
  Purchase #2 $200.47   11.840%   $224.2056   $224.21   $224.20   $224.20  
  Purchase #3 $230.83   9.327%   $252.3595   $252.36   $252.35   $252.40  
  Purchase #4 $27.72   3.113%   $28.5829   $28.58   $28.60   $28.60  
  Purchase #5 $84.30   4.350%   $87.9671   $87.97   $87.95   $88.00  
  Purchase #6 $212.25   8.430%   $230.1427   $230.14   $230.15   $230.10  
  Purchase #7 $182.91   11.653%   $204.2245   $204.22   $204.20   $204.20  
  7 purchase totals = $984.94       $1,077.9490   $1,077.95   $1,077.90   $1,078.00