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 $58.58   4.151%   $61.0117   $61.01   $61.00   $61.00  
  Purchase #2 $110.77   5.326%   $116.6696   $116.67   $116.65   $116.70  
  Purchase #3 $203.85   5.744%   $215.5591   $215.56   $215.55   $215.60  
  Purchase #4 $12.45   6.754%   $13.2909   $13.29   $13.30   $13.30  
  Purchase #5 $55.74   4.761%   $58.3938   $58.39   $58.40   $58.40  
  Purchase #6 $186.90   4.166%   $194.6863   $194.69   $194.70   $194.70  
  Purchase #7 $49.93   12.471%   $56.1568   $56.16   $56.15   $56.20  
  7 purchase totals = $678.22       $715.7682   $715.77   $715.75   $715.90