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 $68.42   3.637%   $70.9084   $70.91   $70.90   $70.90  
  Purchase #2 $118.52   3.501%   $122.6694   $122.67   $122.65   $122.70  
  Purchase #3 $49.43   8.588%   $53.675   $53.68   $53.70   $53.70  
  Purchase #4 $131.38   11.793%   $146.8736   $146.87   $146.85   $146.90  
  Purchase #5 $119.75   9.757%   $131.434   $131.43   $131.45   $131.40  
  Purchase #6 $169.67   4.662%   $177.58   $177.58   $177.60   $177.60  
  Purchase #7 $131.53   9.340%   $143.8149   $143.81   $143.80   $143.80  
  7 purchase totals = $788.70       $846.9553   $846.95   $846.95   $847.00