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 $59.83   8.666%   $65.0149   $65.01   $65.00   $65.00  
  Purchase #2 $232.32   12.751%   $261.9431   $261.94   $261.95   $261.90  
  Purchase #3 $222.49   10.381%   $245.5867   $245.59   $245.60   $245.60  
  Purchase #4 $230.43   10.704%   $255.0952   $255.10   $255.10   $255.10  
  Purchase #5 $238.55   8.633%   $259.144   $259.14   $259.15   $259.10  
  Purchase #6 $28.88   5.768%   $30.5458   $30.55   $30.55   $30.50  
  Purchase #7 $51.59   11.370%   $57.4558   $57.46   $57.45   $57.50  
  7 purchase totals = $1,064.09       $1,174.7855   $1,174.79   $1,174.80   $1,174.70