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 $163.71   5.757%   $173.1348   $173.13   $173.15   $173.10  
  Purchase #2 $63.93   5.326%   $67.3349   $67.33   $67.35   $67.30  
  Purchase #3 $8.42   5.783%   $8.9069   $8.91   $8.90   $8.90  
  Purchase #4 $87.52   5.331%   $92.1857   $92.19   $92.20   $92.20  
  Purchase #5 $226.33   3.250%   $233.6857   $233.69   $233.70   $233.70  
  Purchase #6 $106.88   8.663%   $116.139   $116.14   $116.15   $116.10  
  Purchase #7 $68.81   8.368%   $74.568   $74.57   $74.55   $74.60  
  7 purchase totals = $725.60       $765.9550   $765.96   $766.00   $765.90