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 $220.46   10.542%   $243.7009   $243.70   $243.70   $243.70  
  Purchase #2 $105.62   11.379%   $117.6385   $117.64   $117.65   $117.60  
  Purchase #3 $136.36   13.460%   $154.7141   $154.71   $154.70   $154.70  
  Purchase #4 $54.60   3.654%   $56.5951   $56.60   $56.60   $56.60  
  Purchase #5 $81.71   11.607%   $91.1941   $91.19   $91.20   $91.20  
  Purchase #6 $136.84   12.464%   $153.8957   $153.90   $153.90   $153.90  
  Purchase #7 $228.67   4.847%   $239.7536   $239.75   $239.75   $239.80  
  7 purchase totals = $964.26       $1,057.4920   $1,057.49   $1,057.50   $1,057.50