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 $246.62   6.629%   $262.9684   $262.97   $262.95   $263.00  
  Purchase #2 $211.36   11.643%   $235.9686   $235.97   $235.95   $236.00  
  Purchase #3 $74.38   9.623%   $81.5376   $81.54   $81.55   $81.50  
  Purchase #4 $51.64   8.291%   $55.9215   $55.92   $55.90   $55.90  
  Purchase #5 $201.66   9.563%   $220.9447   $220.94   $220.95   $220.90  
  Purchase #6 $209.85   8.787%   $228.2895   $228.29   $228.30   $228.30  
  Purchase #7 $63.72   12.518%   $71.6965   $71.70   $71.70   $71.70  
  7 purchase totals = $1,059.23       $1,157.3268   $1,157.33   $1,157.30   $1,157.30