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 $136.60   13.417%   $154.9276   $154.93   $154.95   $154.90  
  Purchase #2 $239.43   7.560%   $257.5309   $257.53   $257.55   $257.50  
  Purchase #3 $181.29   10.273%   $199.9139   $199.91   $199.90   $199.90  
  Purchase #4 $14.77   4.866%   $15.4887   $15.49   $15.50   $15.50  
  Purchase #5 $68.80   9.824%   $75.5589   $75.56   $75.55   $75.60  
  Purchase #6 $229.34   7.287%   $246.052   $246.05   $246.05   $246.10  
  Purchase #7 $59.66   5.751%   $63.091   $63.09   $63.10   $63.10  
  7 purchase totals = $929.89       $1,012.5630   $1,012.56   $1,012.60   $1,012.60