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 $132.59   12.513%   $149.181   $149.18   $149.20   $149.20  
  Purchase #2 $85.64   12.314%   $96.1857   $96.19   $96.20   $96.20  
  Purchase #3 $152.54   7.287%   $163.6556   $163.66   $163.65   $163.70  
  Purchase #4 $90.80   12.559%   $102.2036   $102.20   $102.20   $102.20  
  Purchase #5 $101.52   13.354%   $115.077   $115.08   $115.10   $115.10  
  Purchase #6 $119.45   9.866%   $131.2349   $131.23   $131.25   $131.20  
  Purchase #7 $246.81   4.821%   $258.7087   $258.71   $258.70   $258.70  
  7 purchase totals = $929.35       $1,016.2465   $1,016.25   $1,016.30   $1,016.30