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 $63.42   3.367%   $65.5554   $65.56   $65.55   $65.60  
  Purchase #2 $120.81   9.807%   $132.6578   $132.66   $132.65   $132.70  
  Purchase #3 $48.86   12.735%   $55.0823   $55.08   $55.10   $55.10  
  Purchase #4 $238.80   3.222%   $246.4941   $246.49   $246.50   $246.50  
  Purchase #5 $237.81   13.141%   $269.0606   $269.06   $269.05   $269.10  
  Purchase #6 $175.88   6.644%   $187.5655   $187.57   $187.55   $187.60  
  Purchase #7 $106.43   9.440%   $116.477   $116.48   $116.50   $116.50  
  7 purchase totals = $992.01       $1,072.8927   $1,072.90   $1,072.90   $1,073.10