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 $58.54   6.304%   $62.2304   $62.23   $62.25   $62.20  
  Purchase #2 $191.66   6.314%   $203.7614   $203.76   $203.75   $203.80  
  Purchase #3 $139.52   6.852%   $149.0799   $149.08   $149.10   $149.10  
  Purchase #4 $177.67   4.419%   $185.5212   $185.52   $185.50   $185.50  
  Purchase #5 $32.94   6.742%   $35.1608   $35.16   $35.15   $35.20  
  Purchase #6 $121.49   13.751%   $138.1961   $138.20   $138.20   $138.20  
  Purchase #7 $30.77   6.247%   $32.6922   $32.69   $32.70   $32.70  
  7 purchase totals = $752.59       $806.6420   $806.64   $806.65   $806.70