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 $167.86   6.609%   $178.9539   $178.95   $178.95   $179.00  
  Purchase #2 $112.54   12.364%   $126.4544   $126.45   $126.45   $126.50  
  Purchase #3 $231.25   12.224%   $259.518   $259.52   $259.50   $259.50  
  Purchase #4 $207.61   13.311%   $235.245   $235.25   $235.25   $235.20  
  Purchase #5 $53.25   9.630%   $58.378   $58.38   $58.40   $58.40  
  Purchase #6 $31.68   12.720%   $35.7097   $35.71   $35.70   $35.70  
  Purchase #7 $105.45   13.143%   $119.3093   $119.31   $119.30   $119.30  
  7 purchase totals = $909.64       $1,013.5683   $1,013.57   $1,013.55   $1,013.60