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 $230.94   8.120%   $249.6923   $249.69   $249.70   $249.70  
  Purchase #2 $233.90   7.576%   $251.6203   $251.62   $251.60   $251.60  
  Purchase #3 $247.55   8.334%   $268.1808   $268.18   $268.20   $268.20  
  Purchase #4 $78.58   9.173%   $85.7881   $85.79   $85.80   $85.80  
  Purchase #5 $151.81   3.229%   $156.7119   $156.71   $156.70   $156.70  
  Purchase #6 $23.79   12.229%   $26.6993   $26.70   $26.70   $26.70  
  Purchase #7 $14.35   7.272%   $15.3935   $15.39   $15.40   $15.40  
  7 purchase totals = $980.92       $1,054.0862   $1,054.08   $1,054.10   $1,054.10