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 $167.79   5.455%   $176.9429   $176.94   $176.95   $176.90  
  Purchase #2 $179.45   13.464%   $203.6111   $203.61   $203.60   $203.60  
  Purchase #3 $176.61   13.788%   $200.961   $200.96   $200.95   $201.00  
  Purchase #4 $62.97   7.290%   $67.5605   $67.56   $67.55   $67.60  
  Purchase #5 $175.55   11.647%   $195.9963   $196.00   $196.00   $196.00  
  Purchase #6 $96.53   13.633%   $109.6899   $109.69   $109.70   $109.70  
  Purchase #7 $169.70   8.553%   $184.2144   $184.21   $184.20   $184.20  
  7 purchase totals = $1,028.60       $1,138.9761   $1,138.97   $1,138.95   $1,139.00