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 $241.74   11.285%   $269.0204   $269.02   $269.00   $269.00  
  Purchase #2 $62.66   5.679%   $66.2185   $66.22   $66.20   $66.20  
  Purchase #3 $250.55   9.641%   $274.7055   $274.71   $274.70   $274.70  
  Purchase #4 $204.69   7.217%   $219.4625   $219.46   $219.45   $219.50  
  Purchase #5 $163.70   3.331%   $169.1528   $169.15   $169.15   $169.20  
  Purchase #6 $99.95   6.658%   $106.6047   $106.60   $106.60   $106.60  
  Purchase #7 $25.89   5.413%   $27.2914   $27.29   $27.30   $27.30  
  7 purchase totals = $1,049.18       $1,132.4558   $1,132.45   $1,132.40   $1,132.50