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 $144.89   7.777%   $156.1581   $156.16   $156.15   $156.20  
  Purchase #2 $117.65   9.411%   $128.722   $128.72   $128.70   $128.70  
  Purchase #3 $37.79   11.356%   $42.0814   $42.08   $42.10   $42.10  
  Purchase #4 $41.57   8.585%   $45.1388   $45.14   $45.15   $45.10  
  Purchase #5 $22.58   5.867%   $23.9048   $23.90   $23.90   $23.90  
  Purchase #6 $26.26   10.345%   $28.9766   $28.98   $29.00   $29.00  
  Purchase #7 $5.59   8.632%   $6.0725   $6.07   $6.05   $6.10  
  7 purchase totals = $396.33       $431.0542   $431.05   $431.05   $431.10