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 $240.53   10.726%   $266.3292   $266.33   $266.35   $266.30  
  Purchase #2 $197.97   7.372%   $212.5643   $212.56   $212.55   $212.60  
  Purchase #3 $28.55   7.184%   $30.601   $30.60   $30.60   $30.60  
  Purchase #4 $196.97   3.496%   $203.8561   $203.86   $203.85   $203.90  
  Purchase #5 $171.97   6.109%   $182.4756   $182.48   $182.50   $182.50  
  Purchase #6 $124.40   6.524%   $132.5159   $132.52   $132.50   $132.50  
  Purchase #7 $104.70   3.546%   $108.4127   $108.41   $108.40   $108.40  
  7 purchase totals = $1,065.09       $1,136.7548   $1,136.76   $1,136.75   $1,136.80