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 $176.26   5.702%   $186.3103   $186.31   $186.30   $186.30  
  Purchase #2 $62.77   11.172%   $69.7827   $69.78   $69.80   $69.80  
  Purchase #3 $146.37   5.539%   $154.4774   $154.48   $154.50   $154.50  
  Purchase #4 $85.71   10.848%   $95.0078   $95.01   $95.00   $95.00  
  Purchase #5 $207.63   6.751%   $221.6471   $221.65   $221.65   $221.60  
  Purchase #6 $179.42   11.594%   $200.222   $200.22   $200.20   $200.20  
  Purchase #7 $57.96   12.166%   $65.0114   $65.01   $65.00   $65.00  
  7 purchase totals = $916.12       $992.4587   $992.46   $992.45   $992.40