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 $57.59   13.313%   $65.257   $65.26   $65.25   $65.30  
  Purchase #2 $204.89   3.161%   $211.3666   $211.37   $211.35   $211.40  
  Purchase #3 $249.57   5.579%   $263.4935   $263.49   $263.50   $263.50  
  Purchase #4 $222.94   5.322%   $234.8049   $234.80   $234.80   $234.80  
  Purchase #5 $185.59   6.480%   $197.6162   $197.62   $197.60   $197.60  
  Purchase #6 $7.98   13.749%   $9.0772   $9.08   $9.10   $9.10  
  Purchase #7 $241.71   5.782%   $255.6857   $255.69   $255.70   $255.70  
  7 purchase totals = $1,170.27       $1,237.3011   $1,237.31   $1,237.30   $1,237.40