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 $211.35   11.798%   $236.2851   $236.29   $236.30   $236.30  
  Purchase #2 $13.31   9.727%   $14.6047   $14.60   $14.60   $14.60  
  Purchase #3 $160.52   8.631%   $174.3745   $174.37   $174.35   $174.40  
  Purchase #4 $94.89   10.514%   $104.8667   $104.87   $104.85   $104.90  
  Purchase #5 $132.77   4.411%   $138.6265   $138.63   $138.65   $138.60  
  Purchase #6 $103.84   12.757%   $117.0869   $117.09   $117.10   $117.10  
  Purchase #7 $196.61   8.239%   $212.8087   $212.81   $212.80   $212.80  
  7 purchase totals = $913.29       $998.6531   $998.66   $998.65   $998.70