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 $131.53   3.511%   $136.148   $136.15   $136.15   $136.10  
  Purchase #2 $63.77   9.697%   $69.9538   $69.95   $69.95   $70.00  
  Purchase #3 $66.56   6.269%   $70.7326   $70.73   $70.75   $70.70  
  Purchase #4 $36.83   7.798%   $39.702   $39.70   $39.70   $39.70  
  Purchase #5 $49.28   5.841%   $52.1584   $52.16   $52.15   $52.20  
  Purchase #6 $111.37   12.148%   $124.8992   $124.90   $124.90   $124.90  
  Purchase #7 $97.74   4.421%   $102.0611   $102.06   $102.05   $102.10  
  7 purchase totals = $557.08       $595.6551   $595.65   $595.65   $595.70