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 $117.84   5.322%   $124.1114   $124.11   $124.10   $124.10  
  Purchase #2 $178.29   10.335%   $196.7163   $196.72   $196.70   $196.70  
  Purchase #3 $163.77   4.521%   $171.174   $171.17   $171.15   $171.20  
  Purchase #4 $157.90   7.316%   $169.452   $169.45   $169.45   $169.50  
  Purchase #5 $34.49   8.243%   $37.333   $37.33   $37.35   $37.30  
  Purchase #6 $232.70   10.527%   $257.1963   $257.20   $257.20   $257.20  
  Purchase #7 $186.86   8.755%   $203.2196   $203.22   $203.20   $203.20  
  7 purchase totals = $1,071.85       $1,159.2026   $1,159.20   $1,159.15   $1,159.20