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 $156.56   12.754%   $176.5277   $176.53   $176.55   $176.50  
  Purchase #2 $164.53   9.248%   $179.7457   $179.75   $179.75   $179.70  
  Purchase #3 $167.29   7.796%   $180.3319   $180.33   $180.35   $180.30  
  Purchase #4 $57.33   6.252%   $60.9143   $60.91   $60.90   $60.90  
  Purchase #5 $208.80   12.700%   $235.3176   $235.32   $235.30   $235.30  
  Purchase #6 $219.65   13.346%   $248.9645   $248.96   $248.95   $249.00  
  Purchase #7 $207.68   4.290%   $216.5895   $216.59   $216.60   $216.60  
  7 purchase totals = $1,181.84       $1,298.3912   $1,298.39   $1,298.40   $1,298.30