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 $181.78   4.419%   $189.8129   $189.81   $189.80   $189.80  
  Purchase #2 $182.78   9.639%   $200.3982   $200.40   $200.40   $200.40  
  Purchase #3 $6.89   8.263%   $7.4593   $7.46   $7.45   $7.50  
  Purchase #4 $167.26   7.844%   $180.3799   $180.38   $180.40   $180.40  
  Purchase #5 $202.26   10.252%   $222.9957   $223.00   $223.00   $223.00  
  Purchase #6 $100.40   7.125%   $107.5535   $107.55   $107.55   $107.60  
  Purchase #7 $29.41   12.537%   $33.0971   $33.10   $33.10   $33.10  
  7 purchase totals = $870.78       $941.6966   $941.70   $941.70   $941.80