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 $48.78   10.331%   $53.8195   $53.82   $53.80   $53.80  
  Purchase #2 $101.68   4.579%   $106.3359   $106.34   $106.35   $106.30  
  Purchase #3 $169.99   4.665%   $177.92   $177.92   $177.90   $177.90  
  Purchase #4 $179.64   7.775%   $193.607   $193.61   $193.60   $193.60  
  Purchase #5 $123.45   6.180%   $131.0792   $131.08   $131.10   $131.10  
  Purchase #6 $122.77   12.527%   $138.1494   $138.15   $138.15   $138.10  
  Purchase #7 $64.56   6.800%   $68.9501   $68.95   $68.95   $69.00  
  7 purchase totals = $810.87       $869.8611   $869.87   $869.85   $869.80