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 $184.94   12.115%   $207.3455   $207.35   $207.35   $207.30  
  Purchase #2 $167.92   11.162%   $186.6632   $186.66   $186.65   $186.70  
  Purchase #3 $17.40   11.215%   $19.3514   $19.35   $19.35   $19.40  
  Purchase #4 $204.52   6.523%   $217.8608   $217.86   $217.85   $217.90  
  Purchase #5 $20.89   10.223%   $23.0256   $23.03   $23.05   $23.00  
  Purchase #6 $146.59   8.490%   $159.0355   $159.04   $159.05   $159.00  
  Purchase #7 $242.53   12.210%   $272.1429   $272.14   $272.15   $272.10  
  7 purchase totals = $984.79       $1,085.4249   $1,085.43   $1,085.45   $1,085.40