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 $50.82   11.356%   $56.5911   $56.59   $56.60   $56.60  
  Purchase #2 $115.84   9.336%   $126.6548   $126.65   $126.65   $126.70  
  Purchase #3 $235.54   11.237%   $262.0076   $262.01   $262.00   $262.00  
  Purchase #4 $187.92   12.738%   $211.8572   $211.86   $211.85   $211.90  
  Purchase #5 $185.35   3.356%   $191.5703   $191.57   $191.55   $191.60  
  Purchase #6 $243.94   12.152%   $273.5836   $273.58   $273.60   $273.60  
  Purchase #7 $141.52   5.245%   $148.9427   $148.94   $148.95   $148.90  
  7 purchase totals = $1,160.93       $1,271.2073   $1,271.20   $1,271.20   $1,271.30