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 $32.62   7.407%   $35.0362   $35.04   $35.05   $35.00  
  Purchase #2 $215.67   9.511%   $236.1824   $236.18   $236.20   $236.20  
  Purchase #3 $218.54   3.792%   $226.827   $226.83   $226.85   $226.80  
  Purchase #4 $58.28   12.494%   $65.5615   $65.56   $65.55   $65.60  
  Purchase #5 $155.77   3.157%   $160.6877   $160.69   $160.70   $160.70  
  Purchase #6 $30.71   12.586%   $34.5752   $34.58   $34.60   $34.60  
  Purchase #7 $134.64   11.373%   $149.9526   $149.95   $149.95   $150.00  
  7 purchase totals = $846.23       $908.8226   $908.83   $908.90   $908.90