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 $232.29   4.838%   $243.5282   $243.53   $243.55   $243.50  
  Purchase #2 $241.51   8.529%   $262.1084   $262.11   $262.10   $262.10  
  Purchase #3 $65.98   12.450%   $74.1945   $74.19   $74.20   $74.20  
  Purchase #4 $60.96   11.542%   $67.996   $68.00   $68.00   $68.00  
  Purchase #5 $27.62   3.646%   $28.627   $28.63   $28.65   $28.60  
  Purchase #6 $106.70   13.704%   $121.3222   $121.32   $121.30   $121.30  
  Purchase #7 $97.60   9.718%   $107.0848   $107.08   $107.10   $107.10  
  7 purchase totals = $832.66       $904.8611   $904.86   $904.90   $904.80