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 $235.47   11.798%   $263.2508   $263.25   $263.25   $263.30  
  Purchase #2 $203.77   7.858%   $219.7822   $219.78   $219.80   $219.80  
  Purchase #3 $64.95   7.646%   $69.9161   $69.92   $69.90   $69.90  
  Purchase #4 $246.61   3.235%   $254.5878   $254.59   $254.60   $254.60  
  Purchase #5 $218.25   10.535%   $241.2426   $241.24   $241.25   $241.20  
  Purchase #6 $58.46   3.153%   $60.3032   $60.30   $60.30   $60.30  
  Purchase #7 $148.40   3.435%   $153.4975   $153.50   $153.50   $153.50  
  7 purchase totals = $1,175.91       $1,262.5802   $1,262.58   $1,262.60   $1,262.60