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 $141.98   3.242%   $146.583   $146.58   $146.60   $146.60  
  Purchase #2 $9.96   5.679%   $10.5256   $10.53   $10.55   $10.50  
  Purchase #3 $161.49   9.597%   $176.9882   $176.99   $177.00   $177.00  
  Purchase #4 $84.65   6.541%   $90.187   $90.19   $90.20   $90.20  
  Purchase #5 $247.94   10.753%   $274.601   $274.60   $274.60   $274.60  
  Purchase #6 $125.37   12.183%   $140.6438   $140.64   $140.65   $140.60  
  Purchase #7 $47.94   11.506%   $53.456   $53.46   $53.45   $53.50  
  7 purchase totals = $819.33       $892.9846   $892.99   $893.05   $893.00