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 $214.57   10.755%   $237.647   $237.65   $237.65   $237.60  
  Purchase #2 $65.73   4.111%   $68.4322   $68.43   $68.45   $68.40  
  Purchase #3 $55.64   4.393%   $58.0843   $58.08   $58.10   $58.10  
  Purchase #4 $167.26   8.459%   $181.4085   $181.41   $181.40   $181.40  
  Purchase #5 $62.77   5.113%   $65.9794   $65.98   $66.00   $66.00  
  Purchase #6 $25.28   5.617%   $26.7   $26.70   $26.70   $26.70  
  Purchase #7 $16.51   12.845%   $18.6307   $18.63   $18.65   $18.60  
  7 purchase totals = $607.76       $656.8821   $656.88   $656.95   $656.80