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 $231.32   9.823%   $254.0426   $254.04   $254.05   $254.00  
  Purchase #2 $199.96   9.294%   $218.5443   $218.54   $218.55   $218.50  
  Purchase #3 $176.67   7.291%   $189.551   $189.55   $189.55   $189.60  
  Purchase #4 $56.41   9.419%   $61.7233   $61.72   $61.70   $61.70  
  Purchase #5 $249.47   7.549%   $268.3025   $268.30   $268.30   $268.30  
  Purchase #6 $78.40   5.263%   $82.5262   $82.53   $82.55   $82.50  
  Purchase #7 $113.86   12.773%   $128.4033   $128.40   $128.40   $128.40  
  7 purchase totals = $1,106.09       $1,203.0932   $1,203.08   $1,203.10   $1,203.00