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 $210.36   11.671%   $234.9111   $234.91   $234.90   $234.90  
  Purchase #2 $249.43   9.378%   $272.8215   $272.82   $272.80   $272.80  
  Purchase #3 $14.95   10.223%   $16.4783   $16.48   $16.50   $16.50  
  Purchase #4 $148.29   7.169%   $158.9209   $158.92   $158.90   $158.90  
  Purchase #5 $74.58   10.788%   $82.6257   $82.63   $82.65   $82.60  
  Purchase #6 $193.67   13.610%   $220.0285   $220.03   $220.05   $220.00  
  Purchase #7 $203.28   9.756%   $223.112   $223.11   $223.10   $223.10  
  7 purchase totals = $1,094.56       $1,208.8980   $1,208.90   $1,208.90   $1,208.80