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 $199.77   11.758%   $223.259   $223.26   $223.25   $223.30  
  Purchase #2 $239.88   10.662%   $265.456   $265.46   $265.45   $265.50  
  Purchase #3 $43.94   10.290%   $48.4614   $48.46   $48.45   $48.50  
  Purchase #4 $153.46   6.233%   $163.0252   $163.03   $163.05   $163.00  
  Purchase #5 $165.79   9.407%   $181.3859   $181.39   $181.40   $181.40  
  Purchase #6 $116.50   8.761%   $126.7066   $126.71   $126.70   $126.70  
  Purchase #7 $37.90   3.168%   $39.1007   $39.10   $39.10   $39.10  
  7 purchase totals = $957.24       $1,047.3948   $1,047.41   $1,047.40   $1,047.50