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 $246.71   5.665%   $260.6861   $260.69   $260.70   $260.70  
  Purchase #2 $152.47   4.331%   $159.0735   $159.07   $159.05   $159.10  
  Purchase #3 $203.32   12.467%   $228.6679   $228.67   $228.65   $228.70  
  Purchase #4 $185.87   8.253%   $201.2099   $201.21   $201.20   $201.20  
  Purchase #5 $196.40   7.193%   $210.5271   $210.53   $210.55   $210.50  
  Purchase #6 $241.26   5.132%   $253.6415   $253.64   $253.65   $253.60  
  Purchase #7 $149.91   8.373%   $162.462   $162.46   $162.45   $162.50  
  7 purchase totals = $1,375.94       $1,476.2680   $1,476.27   $1,476.25   $1,476.30