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 $25.61   3.487%   $26.503   $26.50   $26.50   $26.50  
  Purchase #2 $172.39   10.297%   $190.141   $190.14   $190.15   $190.10  
  Purchase #3 $233.90   12.654%   $263.4977   $263.50   $263.50   $263.50  
  Purchase #4 $163.61   6.670%   $174.5228   $174.52   $174.50   $174.50  
  Purchase #5 $197.71   11.265%   $219.982   $219.98   $220.00   $220.00  
  Purchase #6 $80.50   10.175%   $88.6909   $88.69   $88.70   $88.70  
  Purchase #7 $247.59   12.483%   $278.4967   $278.50   $278.50   $278.50  
  7 purchase totals = $1,121.31       $1,241.8341   $1,241.83   $1,241.85   $1,241.80