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 $240.74   7.872%   $259.6911   $259.69   $259.70   $259.70  
  Purchase #2 $247.52   9.366%   $270.7027   $270.70   $270.70   $270.70  
  Purchase #3 $59.26   3.790%   $61.506   $61.51   $61.50   $61.50  
  Purchase #4 $147.67   4.166%   $153.8219   $153.82   $153.80   $153.80  
  Purchase #5 $152.89   6.339%   $162.5817   $162.58   $162.60   $162.60  
  Purchase #6 $201.69   5.851%   $213.4909   $213.49   $213.50   $213.50  
  Purchase #7 $204.59   10.391%   $225.8489   $225.85   $225.85   $225.80  
  7 purchase totals = $1,254.36       $1,347.6432   $1,347.64   $1,347.65   $1,347.60