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 $63.68   10.659%   $70.4677   $70.47   $70.45   $70.50  
  Purchase #2 $223.52   13.115%   $252.8346   $252.83   $252.85   $252.80  
  Purchase #3 $249.74   4.533%   $261.0607   $261.06   $261.05   $261.10  
  Purchase #4 $199.82   12.784%   $225.365   $225.37   $225.35   $225.40  
  Purchase #5 $239.88   11.813%   $268.217   $268.22   $268.20   $268.20  
  Purchase #6 $231.86   9.209%   $253.212   $253.21   $253.20   $253.20  
  Purchase #7 $104.44   10.634%   $115.5461   $115.55   $115.55   $115.50  
  7 purchase totals = $1,312.94       $1,446.7031   $1,446.71   $1,446.65   $1,446.70