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 $181.49   6.673%   $193.6008   $193.60   $193.60   $193.60  
  Purchase #2 $156.97   9.506%   $171.8916   $171.89   $171.90   $171.90  
  Purchase #3 $75.59   6.730%   $80.6772   $80.68   $80.70   $80.70  
  Purchase #4 $241.34   7.644%   $259.788   $259.79   $259.80   $259.80  
  Purchase #5 $107.40   7.148%   $115.077   $115.08   $115.10   $115.10  
  Purchase #6 $101.53   6.506%   $108.1355   $108.14   $108.15   $108.10  
  Purchase #7 $56.81   11.796%   $63.5113   $63.51   $63.50   $63.50  
  7 purchase totals = $921.13       $992.6814   $992.69   $992.75   $992.70