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 $154.99   9.487%   $169.6939   $169.69   $169.70   $169.70  
  Purchase #2 $243.90   11.340%   $271.5583   $271.56   $271.55   $271.60  
  Purchase #3 $164.65   5.424%   $173.5806   $173.58   $173.60   $173.60  
  Purchase #4 $17.73   4.507%   $18.5291   $18.53   $18.55   $18.50  
  Purchase #5 $236.45   8.820%   $257.3049   $257.30   $257.30   $257.30  
  Purchase #6 $244.52   5.754%   $258.5897   $258.59   $258.60   $258.60  
  Purchase #7 $87.72   7.565%   $94.356   $94.36   $94.35   $94.40  
  7 purchase totals = $1,149.96       $1,243.6125   $1,243.61   $1,243.65   $1,243.70