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 $5.32   10.430%   $5.8749   $5.87   $5.85   $5.90  
  Purchase #2 $173.57   3.564%   $179.756   $179.76   $179.75   $179.80  
  Purchase #3 $173.40   3.857%   $180.088   $180.09   $180.10   $180.10  
  Purchase #4 $198.55   6.786%   $212.0236   $212.02   $212.00   $212.00  
  Purchase #5 $32.70   11.671%   $36.5164   $36.52   $36.50   $36.50  
  Purchase #6 $156.35   6.516%   $166.5378   $166.54   $166.55   $166.50  
  Purchase #7 $88.58   11.234%   $98.5311   $98.53   $98.55   $98.50  
  7 purchase totals = $828.47       $879.3278   $879.33   $879.30   $879.30