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 $123.43   6.782%   $131.801   $131.80   $131.80   $131.80  
  Purchase #2 $36.98   6.422%   $39.3549   $39.35   $39.35   $39.40  
  Purchase #3 $24.69   6.814%   $26.3724   $26.37   $26.35   $26.40  
  Purchase #4 $29.94   12.266%   $33.6124   $33.61   $33.60   $33.60  
  Purchase #5 $233.69   10.371%   $257.926   $257.93   $257.95   $257.90  
  Purchase #6 $249.71   11.134%   $277.5127   $277.51   $277.50   $277.50  
  Purchase #7 $56.49   4.277%   $58.9061   $58.91   $58.90   $58.90  
  7 purchase totals = $754.93       $825.4855   $825.48   $825.45   $825.50