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 $134.48   12.827%   $151.7297   $151.73   $151.75   $151.70  
  Purchase #2 $156.74   13.328%   $177.6303   $177.63   $177.65   $177.60  
  Purchase #3 $42.33   10.185%   $46.6413   $46.64   $46.65   $46.60  
  Purchase #4 $214.90   11.673%   $239.9853   $239.99   $240.00   $240.00  
  Purchase #5 $103.65   4.557%   $108.3733   $108.37   $108.35   $108.40  
  Purchase #6 $244.35   9.678%   $267.9982   $268.00   $268.00   $268.00  
  Purchase #7 $128.49   10.313%   $141.7412   $141.74   $141.75   $141.70  
  7 purchase totals = $1,024.94       $1,134.0993   $1,134.10   $1,134.15   $1,134.00