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 $144.61   6.521%   $154.04   $154.04   $154.05   $154.00  
  Purchase #2 $104.26   4.301%   $108.7442   $108.74   $108.75   $108.70  
  Purchase #3 $119.41   6.304%   $126.9376   $126.94   $126.95   $126.90  
  Purchase #4 $152.81   4.229%   $159.2723   $159.27   $159.25   $159.30  
  Purchase #5 $23.82   11.350%   $26.5236   $26.52   $26.50   $26.50  
  Purchase #6 $63.26   5.401%   $66.6767   $66.68   $66.70   $66.70  
  Purchase #7 $43.81   11.200%   $48.7167   $48.72   $48.70   $48.70  
  7 purchase totals = $651.98       $690.9111   $690.91   $690.90   $690.80