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 $10.44   6.769%   $11.1467   $11.15   $11.15   $11.10  
  Purchase #2 $24.61   4.720%   $25.7716   $25.77   $25.75   $25.80  
  Purchase #3 $26.89   8.190%   $29.0923   $29.09   $29.10   $29.10  
  Purchase #4 $216.92   10.775%   $240.2931   $240.29   $240.30   $240.30  
  Purchase #5 $68.53   4.411%   $71.5529   $71.55   $71.55   $71.60  
  Purchase #6 $233.43   13.214%   $264.2754   $264.28   $264.30   $264.30  
  Purchase #7 $216.60   7.512%   $232.871   $232.87   $232.85   $232.90  
  7 purchase totals = $797.42       $875.0030   $875.00   $875.00   $875.10